fs/fs-writeback.c

/*
 * fs/fs-writeback.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 *
 * Contains all the functions related to writing back and waiting
 * upon dirty inodes against superblocks, and writing back dirty
 * pages against inodes.  ie: data writeback.  Writeout of the
 * inode itself is not handled here.
 *
 * 10Apr2002	Andrew Morton
 *		Split out of fs/inode.c
 *		Additions for address_space-based writeback
 */

#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/kthread.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/tracepoint.h>
#include <linux/device.h>
#include "internal.h"

/*
 * 4MB minimal write chunk size
 */
#define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_CACHE_SHIFT - 10))

struct wb_completion {
	atomic_t		cnt;
#ifdef CONFIG_CGROUP_WRITEBACK
	int			mapping_ret;	/* used by works w/ ->mapping */
#endif
};

/*
 * Passed into wb_writeback(), essentially a subset of writeback_control
 */
struct wb_writeback_work {
	long nr_pages;

	struct super_block *sb;
	unsigned long *older_than_this;

	/*
	 * If ->mapping is set, only that mapping is written out using
	 * do_writepages().  ->mapping_range_{start|end} are meaningful
	 * only in such cases.
	 */
	struct address_space *mapping;
	loff_t mapping_range_start;
	loff_t mapping_range_end;

	enum writeback_sync_modes sync_mode;
	unsigned int tagged_writepages:1;
	unsigned int for_kupdate:1;
	unsigned int range_cyclic:1;
	unsigned int for_background:1;
	unsigned int for_sync:1;	/* sync(2) WB_SYNC_ALL writeback */
	unsigned int auto_free:1;	/* free on completion */
	unsigned int single_wait:1;
	unsigned int single_done:1;
	enum wb_reason reason;		/* why was writeback initiated? */

	struct list_head list;		/* pending work list */
	struct wb_completion *done;	/* set if the caller waits */
};

/*
 * If one wants to wait for one or more wb_writeback_works, each work's
 * ->done should be set to a wb_completion defined using the following
 * macro.  Once all work items are issued with wb_queue_work(), the caller
 * can wait for the completion of all using wb_wait_for_completion().  Work
 * items which are waited upon aren't freed automatically on completion.
 */
#define DEFINE_WB_COMPLETION_ONSTACK(cmpl)				\
	struct wb_completion cmpl = {					\
		.cnt		= ATOMIC_INIT(1),			\
	}

static struct inode_wb_link *dirty_list_to_iwbl(struct list_head *head)
{
	return list_entry(head, struct inode_wb_link, dirty_list);
}

/*
 * Include the creation of the trace points after defining the
 * wb_writeback_work structure and inline functions so that the definition
 * remains local to this file.
 */
#define CREATE_TRACE_POINTS
#include <trace/events/writeback.h>

EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);

static void wb_wakeup(struct bdi_writeback *wb)
{
	spin_lock_bh(&wb->work_lock);
	if (test_bit(WB_registered, &wb->state))
		mod_delayed_work(bdi_wq, &wb->dwork, 0);
	spin_unlock_bh(&wb->work_lock);
}

static void wb_queue_work(struct bdi_writeback *wb,
			  struct wb_writeback_work *work)
{
	trace_writeback_queue(wb->bdi, work);

	spin_lock_bh(&wb->work_lock);
	if (!test_bit(WB_registered, &wb->state)) {
		if (work->single_wait)
			work->single_done = 1;
		goto out_unlock;
	}
	if (work->done)
		atomic_inc(&work->done->cnt);
	list_add_tail(&work->list, &wb->work_list);
	mod_delayed_work(bdi_wq, &wb->dwork, 0);
out_unlock:
	spin_unlock_bh(&wb->work_lock);
}

/**
 * wb_wait_for_completion - wait for completion of bdi_writeback_works
 * @bdi: bdi work items were issued to
 * @done: target wb_completion
 *
 * Wait for one or more work items issued to @bdi with their ->done field
 * set to @done, which should have been defined with
 * DEFINE_WB_COMPLETION_ONSTACK().  This function returns after all such
 * work items are completed.  Work items which are waited upon aren't freed
 * automatically on completion.
 */
static void wb_wait_for_completion(struct backing_dev_info *bdi,
				   struct wb_completion *done)
{
	atomic_dec(&done->cnt);		/* put down the initial count */
	wait_event(bdi->wb_waitq, !atomic_read(&done->cnt));
}

/**
 * iwbl_move_locked - move an inode_wb_link onto a bdi_writeback IO list
 * @iwbl: inode_wb_link to be moved
 * @wb: target bdi_writeback
 * @head: one of @wb->b_{dirty|io|more_io}
 *
 * Move @iwbl->dirty_list to @list of @wb and set %WB_has_dirty_io.
 * Returns %true if all IO lists were empty before; otherwise, %false.
 */
static bool iwbl_move_locked(struct inode_wb_link *iwbl,
			     struct bdi_writeback *wb, struct list_head *head)
{
	assert_spin_locked(&wb->list_lock);

	list_move(&iwbl->dirty_list, head);

	if (wb_has_dirty_io(wb)) {
		return false;
	} else {
		set_bit(WB_has_dirty_io, &wb->state);
		WARN_ON_ONCE(!wb->avg_write_bandwidth);
		atomic_long_add(wb->avg_write_bandwidth,
				&wb->bdi->tot_write_bandwidth);
		return true;
	}
}

/**
 * iwbl_del_locked - remove an inode_wb_link from its bdi_writeback IO list
 * @iwbl: inode_wb_link to be removed
 * @wb: bdi_writeback @inode is being removed from
 *
 * Remove @iwbl which may be on one of @wb->b_{dirty|io|more_io} lists and
 * clear %WB_has_dirty_io if all are empty afterwards.
 */
static void iwbl_del_locked(struct inode_wb_link *iwbl,
			    struct bdi_writeback *wb)
{
	assert_spin_locked(&wb->list_lock);

	list_del_init(&iwbl->dirty_list);

	if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
	    list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
		clear_bit(WB_has_dirty_io, &wb->state);
		WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
					&wb->bdi->tot_write_bandwidth) < 0);
	}
}

static void iwbl_del(struct inode_wb_link *iwbl)
{
	struct bdi_writeback *wb = iwbl_to_wb(iwbl);

	if (list_empty(&iwbl->dirty_list))
		return;

	spin_lock(&wb->list_lock);
	iwbl_del_locked(iwbl, wb);
	spin_unlock(&wb->list_lock);
}

/*
 * Wait for writeback on an inode to complete. Called with i_lock held.
 * Caller must make sure inode cannot go away when we drop i_lock.
 */
static void __inode_wait_for_writeback(struct inode *inode)
	__releases(inode->i_lock)
	__acquires(inode->i_lock)
{
	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
	wait_queue_head_t *wqh;

	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
	while (inode->i_state & I_SYNC) {
		spin_unlock(&inode->i_lock);
		__wait_on_bit(wqh, &wq, bit_wait, TASK_UNINTERRUPTIBLE);
		spin_lock(&inode->i_lock);
	}
}

#ifdef CONFIG_CGROUP_WRITEBACK

/**
 * mapping_congested - test whether a mapping is congested for a task
 * @mapping: address space to test for congestion
 * @task: task to test congestion for
 * @bdi_bits: mask of WB_[a]sync_congested bits to test
 *
 * Tests whether @mapping is congested for @task.  @bdi_bits is the mask of
 * congestion bits to test and the return value is the mask of set bits.
 *
 * If cgroup writeback is enabled for @mapping, its congestion state for
 * @task is determined by whether the cgwb (cgroup bdi_writeback) for the
 * blkcg of %current on @mapping->backing_dev_info is congested; otherwise,
 * the root's congestion state is used.
 */
int mapping_congested(struct address_space *mapping,
		      struct task_struct *task, int bdi_bits)
{
	struct backing_dev_info *bdi = mapping->backing_dev_info;
	struct bdi_writeback *wb;
	int ret = 0;

	if (!mapping_cgwb_enabled(mapping))
		return wb_congested(&bdi->wb, bdi_bits);

	rcu_read_lock();
	wb = cgwb_lookup(bdi, task_css(task, blkio_cgrp_id));
	if (wb)
		ret = wb_congested(wb, bdi_bits);
	rcu_read_unlock();

	return ret;
}
EXPORT_SYMBOL_GPL(mapping_congested);

/**
 * init_cgwb_dirty_page_context - init cgwb part of dirty_context
 * @dctx: dirty_context being initialized
 *
 * @dctx is being initialized by init_dirty_page_context().  Initialize
 * cgroup writeback part of it.
 */
static void init_cgwb_dirty_page_context(struct dirty_context *dctx)
{
	struct backing_dev_info *bdi = dctx->mapping->backing_dev_info;
	struct cgroup_subsys_state *blkcg_css;

	/* cgroup writeback requires support from both the bdi and filesystem */
	if (!mapping_cgwb_enabled(dctx->mapping))
		goto force_root;

	/*
	 * @dctx->page is a candidate for cgroup writeback and about to be
	 * dirtied.  Attach the dirty blkcg to the page and pre-allocate
	 * all resources necessary for cgroup writeback.  On failure, fall
	 * back to the root blkcg.
	 */
	blkcg_css = page_blkcg_attach_dirty(dctx->page);

	/* if iwbl already exists, wb can be determined from that too */
	dctx->iwbl = iwbl_lookup(dctx->inode, blkcg_css);
	if (dctx->iwbl) {
		dctx->wb = iwbl_to_wb(dctx->iwbl);
		return;
	}

	/* slow path, let's create wb and iwbl */
	dctx->wb = cgwb_lookup_create(bdi, blkcg_css);
	if (!dctx->wb)
		goto detach_dirty;

	dctx->iwbl = iwbl_create(dctx->inode, dctx->wb);
	if (!dctx->iwbl)
		goto detach_dirty;

	return;

detach_dirty:
	page_blkcg_detach_dirty(dctx->page);
force_root:
	page_blkcg_force_root_dirty(dctx->page);
	dctx->wb = &bdi->wb;
	if (dctx->inode)
		dctx->iwbl = &dctx->inode->i_wb_link;
	else
		dctx->iwbl = NULL;
}

/**
 * wb_wait_for_single_work - wait for completion of a single bdi_writeback_work
 * @bdi: bdi the work item was issued to
 * @work: work item to wait for
 *
 * Wait for the completion of @work which was issued to one of @bdi's
 * bdi_writeback's.  The caller must have set @work->single_wait before
 * issuing it.  This wait operates independently fo
 * wb_wait_for_completion() and also disables automatic freeing of @work.
 */
static void wb_wait_for_single_work(struct backing_dev_info *bdi,
				    struct wb_writeback_work *work)
{
	if (WARN_ON_ONCE(!work->single_wait))
		return;

	wait_event(bdi->wb_waitq, work->single_done);

	/*
	 * Paired with smp_wmb() in wb_do_writeback() and ensures that all
	 * modifications to @work prior to assertion of ->single_done is
	 * visible to the caller once this function returns.
	 */
	smp_rmb();
}

/**
 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
 * @wb: target bdi_writeback to split @nr_pages to
 * @nr_pages: number of pages to write for the whole bdi
 *
 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
 * relation to the total write bandwidth of all wb's w/ dirty inodes on
 * @wb->bdi.
 */
static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
{
	unsigned long this_bw = wb->avg_write_bandwidth;
	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);

	if (nr_pages == LONG_MAX)
		return LONG_MAX;

	/*
	 * This may be called on clean wb's and proportional distribution
	 * may not make sense, just use the original @nr_pages in those
	 * cases.  In general, we wanna err on the side of writing more.
	 */
	if (!tot_bw || this_bw >= tot_bw)
		return nr_pages;
	else
		return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
}

/**
 * wb_clone_and_queue_work - clone a wb_writeback_work and issue it to a wb
 * @wb: target bdi_writeback
 * @base_work: source wb_writeback_work
 *
 * Try to make a clone of @base_work and issue it to @wb.  If cloning
 * succeeds, %true is returned; otherwise, @base_work is issued directly
 * and %false is returned.  In the latter case, the caller is required to
 * wait for @base_work's completion using wb_wait_for_single_work().
 *
 * A clone is auto-freed on completion.  @base_work never is.
 */
static bool wb_clone_and_queue_work(struct bdi_writeback *wb,
				    struct wb_writeback_work *base_work)
{
	struct wb_writeback_work *work;

	work = kmalloc(sizeof(*work), GFP_ATOMIC);
	if (work) {
		*work = *base_work;
		work->auto_free = 1;
		work->single_wait = 0;
	} else {
		work = base_work;
		work->auto_free = 0;
		work->single_wait = 1;
	}
	work->single_done = 0;
	wb_queue_work(wb, work);
	return work != base_work;
}

/**
 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
 * @bdi: target backing_dev_info
 * @base_work: wb_writeback_work to issue
 * @skip_if_busy: skip wb's which already have writeback in progress
 *
 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
 * have dirty inodes.  If @base_work->nr_page isn't %LONG_MAX, it's
 * distributed to the busy wbs according to each wb's proportion in the
 * total active write bandwidth of @bdi.
 */
static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
				  struct wb_writeback_work *base_work,
				  bool skip_if_busy)
{
	long nr_pages = base_work->nr_pages;
	int next_blkcg_id = 0;
	struct bdi_writeback *wb;
	struct wb_iter iter;

	might_sleep();

	if (!bdi_has_dirty_io(bdi))
		return;
restart:
	rcu_read_lock();
	bdi_for_each_wb(wb, bdi, &iter, next_blkcg_id) {
		if (!wb_has_dirty_io(wb) ||
		    (skip_if_busy && writeback_in_progress(wb)))
			continue;

		base_work->nr_pages = wb_split_bdi_pages(wb, nr_pages);
		if (!wb_clone_and_queue_work(wb, base_work)) {
			next_blkcg_id = wb->blkcg_css->id + 1;
			rcu_read_unlock();
			wb_wait_for_single_work(bdi, base_work);
			goto restart;
		}
	}
	rcu_read_unlock();
}

/**
 * iwbl_test_sync - test whether writeback is in progress on an inode_wb_link
 * @iwbl: target inode_wb_link
 *
 * Test whether writeback is in progress for the inode on the bdi_writeback
 * specified by @iwbl.  The caller is responsible for synchornization.
 */
static bool iwbl_test_sync(struct inode_wb_link *iwbl)
{
	return test_bit(IWBL_SYNC, &iwbl->data);
}

/**
 * iwbl_set_sync - mark an inode_wb_link that writeback is in progress
 * @iwbl: target inode_wb_link
 * @inode: inode @iwbl is associated with
 *
 * Mark that writeback is in progress for @inode on the bdi_writeback
 * specified by @iwbl.  iwbl_test_sync() will return %true on @iwbl and
 * %I_SYNC is set on @inode while there's any writeback in progress on it.
 */
static void iwbl_set_sync(struct inode_wb_link *iwbl, struct inode *inode)
{
	lockdep_assert_held(&inode->i_lock);
	WARN_ON_ONCE(iwbl_test_sync(iwbl));

	set_bit(IWBL_SYNC, &iwbl->data);
	inode->i_nr_syncs++;
	inode->i_state |= I_SYNC;
}

/**
 * iwbl_clear_sync - undo iwbl_set_sync()
 * @iwbl: target inode_wb_link
 * @inode: inode @iwbl is associated with
 *
 * Returns %true if this was the last writeback in progress on @inode;
 * %false, otherwise.
 */
static bool iwbl_clear_sync(struct inode_wb_link *iwbl, struct inode *inode)
{
	bool sync_complete;

	lockdep_assert_held(&inode->i_lock);
	WARN_ON_ONCE(!iwbl_test_sync(iwbl));

	clear_bit(IWBL_SYNC, &iwbl->data);
	sync_complete = !--inode->i_nr_syncs;
	if (sync_complete)
		inode->i_state &= ~I_SYNC;
	return sync_complete;
}

/**
 * iwbl_wait_for_writeback - wait for writeback in progree on an inode_wb_link
 * @iwbl: target inode_wb_link
 *
 * Wait for the writeback in progress for the inode on the bdi_writeback
 * specified by @iwbl.
 */
static void iwbl_wait_for_writeback(struct inode_wb_link *iwbl)
	__releases(inode->i_lock)
	__acquires(inode->i_lock)
{
	struct inode *inode = iwbl_to_inode(iwbl);
	DEFINE_WAIT_BIT(wq, &iwbl->data, IWBL_SYNC);
	wait_queue_head_t *wqh;

	lockdep_assert_held(&inode->i_lock);

	wqh = bit_waitqueue(&iwbl->data, IWBL_SYNC);
	while (test_bit(IWBL_SYNC, &iwbl->data)) {
		spin_unlock(&inode->i_lock);
		__wait_on_bit(wqh, &wq, bit_wait, TASK_UNINTERRUPTIBLE);
		spin_lock(&inode->i_lock);
	}
}

/*
 * Sleep until I_SYNC is cleared. This function must be called with i_lock
 * held and drops it. It is aimed for callers not holding any inode reference
 * so once i_lock is dropped, inode can go away.
 */
static void iwbl_sleep_on_writeback(struct inode_wb_link *iwbl)
{
	DEFINE_WAIT(wait);
	struct inode *inode = iwbl_to_inode(iwbl);
	wait_queue_head_t *wqh = bit_waitqueue(&iwbl->data, IWBL_SYNC);
	int sleep;

	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
	sleep = test_bit(IWBL_SYNC, &iwbl->data);
	spin_unlock(&inode->i_lock);
	if (sleep)
		schedule();
	finish_wait(wqh, &wait);
}

/**
 * iwbl_sync_wakeup - wakeup iwbl_{wait_for|sleep_on}_writeback() waiter
 * @iwbl: target inode_wb_link
 */
static void iwbl_sync_wakeup(struct inode_wb_link *iwbl)
{
	wake_up_bit(&iwbl->data, IWBL_SYNC);
}

static inline struct inode_cgwb_link *icgwbl_first(struct inode *inode)
{
	struct hlist_node *node =
		rcu_dereference_check(hlist_first_rcu(&inode->i_cgwb_links),
			lockdep_is_held(&inode_to_bdi(inode)->icgwbls_lock));

	return hlist_entry_safe(node, struct inode_cgwb_link, inode_node);
}

static inline struct inode_cgwb_link *icgwbl_next(struct inode_cgwb_link *pos,
						  struct inode *inode)
{
	struct hlist_node *node =
		rcu_dereference_check(hlist_next_rcu(&pos->inode_node),
			lockdep_is_held(&inode_to_bdi(inode)->icgwbls_lock));

	return hlist_entry_safe(node, struct inode_cgwb_link, inode_node);
}

/**
 * inode_for_each_icgwbl - walk all icgwbl's of an inode
 * @cur: cursor struct inode_cgwb_link pointer
 * @nxt: temp struct inode_cgwb_link pointer
 * @inode: inode to walk icgwbl's of
 *
 * Walk @inode's icgwbl's (inode_cgwb_link's).  rcu_read_lock() must be
 * held throughout iteration.
 */
#define inode_for_each_icgwbl(cur, nxt, inode)				\
	for ((cur) = icgwbl_first((inode)),				\
	     (nxt) = (cur) ? icgwbl_next((cur), (inode)) : NULL;	\
	     (cur);							\
	     (cur) = (nxt),						\
	     (nxt) = (nxt) ? icgwbl_next((nxt), (inode)) : NULL)

static void inode_icgwbls_del(struct inode *inode)
{
	LIST_HEAD(to_free);
	struct backing_dev_info *bdi = inode_to_bdi(inode);
	struct inode_cgwb_link *icgwbl, *next;
	unsigned long flags;

	spin_lock_irqsave(&bdi->icgwbls_lock, flags);

	/* I_FREEING must be set here to disallow further iwbl_create() */
	WARN_ON_ONCE(!(inode->i_state & I_FREEING));

	/*
	 * We don't wanna nest wb->list_lock under bdi->icgwbls_lock as the
	 * latter is irq-safe and the former isn't.  Queue icgwbls on
	 * @to_free and perform iwbl_del() and freeing after releasing
	 * bdi->icgwbls_lock.
	 */
	inode_for_each_icgwbl(icgwbl, next, inode) {
		WARN_ON_ONCE(test_bit(IWBL_SYNC, &icgwbl->iwbl.data));
		hlist_del_rcu(&icgwbl->inode_node);
		list_move(&icgwbl->wb_node, &to_free);
	}

	spin_unlock_irqrestore(&bdi->icgwbls_lock, flags);

	list_for_each_entry_safe(icgwbl, next, &to_free, wb_node) {
		iwbl_del(&icgwbl->iwbl);
		kfree_rcu(icgwbl, rcu);
	}
}

/**
 * wbc_set_iwbl - associate a wbc with an iwbl
 * @wbc: target writeback_control
 * @iwbl: inode_wb_link to associate @wbc with
 *
 * Writeback for @iwbl is about to be performed with @wbc as the control
 * structure.  Associate @wbc with @iwbl so that writeback implementation
 * can retrieve @iwbl from @wbc.
 */
static inline void wbc_set_iwbl(struct writeback_control *wbc,
				struct inode_wb_link *iwbl)
{
	wbc->iwbl = iwbl;
}

/**
 * iwbl_has_enough_dirty - does an iwbl and its inode have dirty bits already?
 * @iwbl: inode_wb_link of interest
 * @inode: inode @iwbl belongs to
 * @dirty: I_DIRTY_* bits to be set
 *
 * @inode is being dirtied with @dirty by @iwbl's cgroup, test whether
 * @iwbl and @inode already have all the dirty bits set.  Each iwbl has
 * separate %IWBL_DIRTY_PAGES bit which should be also set if @dirty has
 * %I_DIRTY_PAGES.
 */
static inline bool iwbl_has_enough_dirty(struct inode_wb_link *iwbl,
					 struct inode *inode, int dirty)
{
	return (inode->i_state & dirty) == dirty &&
		(!(dirty & I_DIRTY_PAGES) ||
		 test_bit(IWBL_DIRTY_PAGES, &iwbl->data));
}

/**
 * iwbl_set_dirty - set dirty bits on an iwbl and its inode
 * @iwbl: ionde_wb_link of interest
 * @inode: inode @iwbl belongs to
 * @dirty: I_DIRTY_* bits to be set
 *
 * Set @dirty on @iwbl and @inode and return whether @iwbl was already
 * dirty.  @iwbl only carries the data dirty bit through %IWBL_DIRTY_PAGES.
 */
static inline bool iwbl_set_dirty(struct inode_wb_link *iwbl,
				  struct inode *inode, int dirty)
{
	bool was_dirty = test_bit(IWBL_DIRTY_PAGES, &iwbl->data);

	/* metadata dirty bit is always attributed to the root */
	if (iwbl_is_root(iwbl))
		was_dirty |= inode->i_state & (I_DIRTY_SYNC | I_DIRTY_DATASYNC);

	inode->i_state |= dirty;
	if (dirty & I_DIRTY_PAGES)
		set_bit(IWBL_DIRTY_PAGES, &iwbl->data);
	return was_dirty;
}

/**
 * iwbl_still_has_dirty_pages - does an iwbl have dirty pages after writeback?
 * @iwbl: inode_wb_link of interest
 * @inode: inode @iwbl belongs to
 *
 * Called from requeue_inode() after writing back @inode for @iwbl to
 * determine whether @iwbl still has dirty pages and should thus be
 * requeued.  This function can update IWBL_DIRTY_PAGES and may also
 * spuriously return true.
 *
 * See IWBL_DIRTY_PAGES definition for more info.
 */
static inline bool iwbl_still_has_dirty_pages(struct inode_wb_link *iwbl,
					      struct inode *inode)
{
	if (!mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
		clear_bit(IWBL_DIRTY_PAGES, &iwbl->data);
		return false;
	}
	return test_bit(IWBL_DIRTY_PAGES, &iwbl->data);
}

/**
 * wbc_skip_metadata - determine whether to skip writing out metadata
 * @wbc: writeback_control in effect
 *
 * Called by __writeback_single_inode() to decide whether to skip writing
 * out metadata.  Metadata is always dirtied against the root cgroup and
 * should only be written out by the root.
 */
static inline bool wbc_skip_metadata(struct writeback_control *wbc)
{
	return wbc->iwbl && !iwbl_is_root(wbc->iwbl);
}

static bool cgwb_do_writepages_split_work(struct inode_wb_link *iwbl,
					  struct wb_writeback_work *base_work)
{
	struct bdi_writeback *wb = iwbl_to_wb(iwbl);

	/* if DIRTY_PAGES isn't visible yet, neither is the dirty data */
	if (!test_bit(IWBL_DIRTY_PAGES, &iwbl->data))
		return true;

	return wb_clone_and_queue_work(wb, base_work);
}

/**
 * cgwb_do_writepages - cgroup-aware do_writepages()
 * @mapping: address_space to write out
 * @wbc: writeback_control in effect
 *
 * Write out pages from @mapping according to @wbc.  This function expects
 * @mapping to be a file backed one.  If cgroup writeback is enabled, the
 * writes are distributed across the cgroups which dirtied the pages;
 * otherwise, this is equivalent to do_writepages().  Returns 0 on success,
 * -errno on failre.
 */
int cgwb_do_writepages(struct address_space *mapping,
		       struct writeback_control *wbc)
{
	DEFINE_WB_COMPLETION_ONSTACK(done);
	struct inode *inode = mapping->host;
	struct backing_dev_info *bdi = inode_to_bdi(inode);
	struct wb_writeback_work base_work = {
		.mapping		= mapping,
		.mapping_range_start	= wbc->range_start,
		.mapping_range_end	= wbc->range_end,
		.nr_pages		= wbc->nr_to_write,
		.sync_mode		= wbc->sync_mode,
		.tagged_writepages	= wbc->tagged_writepages,
		.for_kupdate		= wbc->for_kupdate,
		.range_cyclic		= wbc->range_cyclic,
		.for_background		= wbc->for_background,
		.for_sync		= wbc->for_sync,
		.done			= &done,
	};
	struct cgroup_subsys_state *blkcg_css;
	struct inode_wb_link *iwbl;
	struct inode_cgwb_link *icgwbl, *n;
	int last_blkcg_id = 0, ret;

	/*
	 * The caller is likely flushing the pages it dirtied.  First look
	 * up the current iwbl and perform do_writepages() directly on it.
	 * If no page is skipped due to mismatching cgroup, there's nothing
	 * more to do.
	 */
	blkcg_css = task_get_css(current, blkio_cgrp_id);
	iwbl = iwbl_lookup(inode, blkcg_css);
	if (iwbl) {
		wbc_set_iwbl(wbc, iwbl);
		wbc->iwbl_mismatch = 0;

		ret = do_writepages(mapping, wbc);

		css_put(blkcg_css);
		if (ret || !wbc->iwbl_mismatch)
			return ret;
	} else {
		css_put(blkcg_css);
	}

	/*
	 * Split writes to all dirty iwbl's.  We don't yet implement
	 * bandwidth-proportional distribution of nr_pages as the only
	 * current caller, __filemap_fdatawrite_range(), always sets it to
	 * LONG_MAX.  Implementing proportional distribution would require
	 * a prepatory pass over dirty iwbl's to calculate the total write
	 * bandwidth of the involved wb's.
	 */
	WARN_ON_ONCE(base_work.nr_pages != LONG_MAX);

	if (!cgwb_do_writepages_split_work(&inode->i_wb_link, &base_work))
		wb_wait_for_single_work(bdi, &base_work);
restart_split:
	rcu_read_lock();
	inode_for_each_icgwbl(icgwbl, n, inode) {
		struct inode_wb_link *iwbl = &icgwbl->iwbl;
		int blkcg_id = iwbl_to_wb(iwbl)->blkcg_css->id;

		if (blkcg_id <= last_blkcg_id)
			continue;

		if (!cgwb_do_writepages_split_work(iwbl, &base_work)) {
			rcu_read_unlock();
			wb_wait_for_single_work(bdi, &base_work);
			goto restart_split;
		}
		last_blkcg_id = blkcg_id;
	}
	rcu_read_unlock();

	wb_wait_for_completion(bdi, &done);
	return done.mapping_ret;
}

static bool maybe_writeback_single_mapping(struct wb_writeback_work *work)
{
	struct wb_completion *done = work->done;
	struct writeback_control wbc = {
		.range_start		= work->mapping_range_start,
		.range_end		= work->mapping_range_end,
		.nr_to_write		= work->nr_pages,
		.sync_mode		= work->sync_mode,
		.tagged_writepages	= work->tagged_writepages,
		.for_kupdate		= work->for_kupdate,
		.range_cyclic		= work->range_cyclic,
		.for_background		= work->for_background,
		.for_sync		= work->for_sync,
	};
	int ret;

	if (!work->mapping)
		return false;

	ret = do_writepages(work->mapping, &wbc);
	if (done && ret)
		done->mapping_ret = ret;
	return true;
}

#else	/* CONFIG_CGROUP_WRITEBACK */

static void init_cgwb_dirty_page_context(struct dirty_context *dctx)
{
	dctx->wb = &dctx->mapping->backing_dev_info->wb;
	dctx->iwbl = dctx->inode ? &dctx->inode->i_wb_link : NULL;
}

static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
{
	return nr_pages;
}

static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
				  struct wb_writeback_work *base_work,
				  bool skip_if_busy)
{
	might_sleep();

	if (bdi_has_dirty_io(bdi) &&
	    (!skip_if_busy || !writeback_in_progress(&bdi->wb))) {
		base_work->auto_free = 0;
		base_work->single_wait = 0;
		base_work->single_done = 0;
		wb_queue_work(&bdi->wb, base_work);
	}
}

static bool iwbl_test_sync(struct inode_wb_link *iwbl)
{
	struct inode *inode = iwbl_to_inode(iwbl);

	return inode->i_state & I_SYNC;
}

static void iwbl_set_sync(struct inode_wb_link *iwbl, struct inode *inode)
{
	inode->i_state |= I_SYNC;
}

static bool iwbl_clear_sync(struct inode_wb_link *iwbl, struct inode *inode)
{
	inode->i_state &= ~I_SYNC;
	return true;
}

static void iwbl_wait_for_writeback(struct inode_wb_link *iwbl)
{
	__inode_wait_for_writeback(iwbl_to_inode(iwbl));
}

/*
 * Sleep until I_SYNC is cleared. This function must be called with i_lock
 * held and drops it. It is aimed for callers not holding any inode reference
 * so once i_lock is dropped, inode can go away.
 */
static void iwbl_sleep_on_writeback(struct inode_wb_link *iwbl)
	__releases(inode->i_lock)
{
	DEFINE_WAIT(wait);
	struct inode *inode = iwbl_to_inode(iwbl);
	wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
	int sleep;

	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
	sleep = inode->i_state & I_SYNC;
	spin_unlock(&inode->i_lock);
	if (sleep)
		schedule();
	finish_wait(wqh, &wait);
}

static void iwbl_sync_wakeup(struct inode_wb_link *iwbl)
{
	/* noop, __I_SYNC wakeup is enough */
}

static void inode_icgwbls_del(struct inode *inode)
{
}

static inline void wbc_set_iwbl(struct writeback_control *wbc,
				struct inode_wb_link *iwbl)
{
}

static inline bool iwbl_has_enough_dirty(struct inode_wb_link *iwbl,
					 struct inode *inode, int dirty)
{
	return (inode->i_state & dirty) == dirty;
}

static inline bool iwbl_set_dirty(struct inode_wb_link *iwbl,
				  struct inode *inode, int dirty)
{
	bool was_dirty = inode->i_state & I_DIRTY;

	inode->i_state |= dirty;
	return was_dirty;
}

static inline bool iwbl_still_has_dirty_pages(struct inode_wb_link *iwbl,
					      struct inode *inode)
{
	return mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY);
}

static inline bool wbc_skip_metadata(struct writeback_control *wbc)
{
	return false;
}

static bool maybe_writeback_single_mapping(struct wb_writeback_work *work)
{
	return false;
}

#endif	/* CONFIG_CGROUP_WRITEBACK */

/**
 * init_dirty_page_context - init dirty_context for page dirtying
 * @dctx: dirty_context to initialize
 * @page: page to be dirtied
 *
 * @page is about to be dirtied, prepare @dctx accordingly.  Must be called
 * with @mapping->tree_lock held.  The inode dirtying due to @page dirtying
 * should use the same @dctx.
 *
 * @mapping may have been obtained before the lock was acquired and
 * @dctx->mapping can be set to NULL even if @mapping isn't if truncate
 * took place in-between.  @dctx->inode is always set to @mapping->inode.
 */
void init_dirty_page_context(struct dirty_context *dctx, struct page *page,
			     struct address_space *mapping)
{
	lockdep_assert_held(&mapping->tree_lock);

	dctx->page = page;
	dctx->inode = mapping->host;
	dctx->mapping = page_mapping(page);

	BUG_ON(dctx->mapping != mapping);

	init_cgwb_dirty_page_context(dctx);
}
EXPORT_SYMBOL_GPL(init_dirty_page_context);

/**
 * init_dirty_inode_context - init dirty_context for inode dirtying
 * @dctx: dirty_context to initialize
 * @inode: inode to be dirtied
 *
 * @inode is about to be dirtied w/o a page belonging to it being dirtied,
 * prepare @dctx accordingly.
 */
void init_dirty_inode_context(struct dirty_context *dctx, struct inode *inode)
{
	memset(dctx, 0, sizeof(*dctx));
	dctx->inode = inode;
	dctx->wb = &inode_to_bdi(inode)->wb;
	dctx->iwbl = &inode->i_wb_link;
}

void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
			bool range_cyclic, enum wb_reason reason)
{
	struct wb_writeback_work *work;

	if (!wb_has_dirty_io(wb))
		return;

	/*
	 * This is WB_SYNC_NONE writeback, so if allocation fails just
	 * wakeup the thread for old dirty data writeback
	 */
	work = kzalloc(sizeof(*work), GFP_ATOMIC);
	if (!work) {
		trace_writeback_nowork(wb->bdi);
		wb_wakeup(wb);
		return;
	}

	work->sync_mode	= WB_SYNC_NONE;
	work->nr_pages	= nr_pages;
	work->range_cyclic = range_cyclic;
	work->reason	= reason;
	work->auto_free	= 1;

	wb_queue_work(wb, work);
}

/**
 * wb_start_background_writeback - start background writeback
 * @wb: bdi_writback to write from
 *
 * Description:
 *   This makes sure WB_SYNC_NONE background writeback happens. When
 *   this function returns, it is only guaranteed that for given wb
 *   some IO is happening if we are over background dirty threshold.
 *   Caller need not hold sb s_umount semaphore.
 */
void wb_start_background_writeback(struct bdi_writeback *wb)
{
	/*
	 * We just wake up the flusher thread. It will perform background
	 * writeback as soon as there is no other work to do.
	 */
	trace_writeback_wake_background(wb->bdi);
	wb_wakeup(wb);
}

/*
 * Remove the inode from the writeback list it is on.
 */
void inode_wb_list_del(struct inode *inode)
{
	iwbl_del(&inode->i_wb_link);
	inode_icgwbls_del(inode);
}

/*
 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
 * furthest end of its superblock's dirty-inode list.
 *
 * Before stamping the iwbl's ->dirtied_when, we check to see whether it is
 * already the most-recently-dirtied inode on the b_dirty list.  If that is
 * the case then the inode must have been redirtied while it was being written
 * out and we don't reset its dirtied_when.
 */
static void redirty_tail(struct inode_wb_link *iwbl, struct bdi_writeback *wb)
{
	if (!list_empty(&wb->b_dirty)) {
		struct inode_wb_link *tail;

		tail = dirty_list_to_iwbl(wb->b_dirty.next);
		if (time_before(iwbl->dirtied_when, tail->dirtied_when))
			iwbl->dirtied_when = jiffies;
	}
	iwbl_move_locked(iwbl, wb, &wb->b_dirty);
}

/*
 * requeue inode for re-scanning after bdi->b_io list is exhausted.
 */
static void requeue_io(struct inode_wb_link *iwbl, struct bdi_writeback *wb)
{
	iwbl_move_locked(iwbl, wb, &wb->b_more_io);
}

static void iwbl_sync_complete(struct inode_wb_link *iwbl)
{
	struct inode *inode = iwbl_to_inode(iwbl);
	bool sync_complete;

	sync_complete = iwbl_clear_sync(iwbl, inode);
	/* If inode is clean an unused, put it into LRU now... */
	if (sync_complete)
		inode_add_lru(inode);

	/* Waiters must see I_SYNC cleared before being woken up */
	smp_mb();

	iwbl_sync_wakeup(iwbl);
	if (sync_complete)
		wake_up_bit(&inode->i_state, __I_SYNC);
}

static bool iwbl_dirtied_after(struct inode_wb_link *iwbl, unsigned long t)
{
	bool ret = time_after(iwbl->dirtied_when, t);
#ifndef CONFIG_64BIT
	/*
	 * For inodes being constantly redirtied, dirtied_when can get stuck.
	 * It _appears_ to be in the future, but is actually in distant past.
	 * This test is necessary to prevent such wrapped-around relative times
	 * from permanently stopping the whole bdi writeback.
	 */
	ret = ret && time_before_eq(iwbl->dirtied_when, jiffies);
#endif
	return ret;
}

/*
 * Move expired (dirtied before work->older_than_this) dirty inodes from
 * @delaying_queue to @dispatch_queue.
 */
static int move_expired_inodes(struct list_head *delaying_queue,
			       struct list_head *dispatch_queue,
			       struct wb_writeback_work *work)
{
	LIST_HEAD(tmp);
	struct list_head *pos, *node;
	struct super_block *sb = NULL;
	struct inode_wb_link *iwbl;
	struct inode *inode;
	int do_sb_sort = 0;
	int moved = 0;

	while (!list_empty(delaying_queue)) {
		iwbl = dirty_list_to_iwbl(delaying_queue->prev);
		inode = iwbl_to_inode(iwbl);

		if (work->older_than_this &&
		    iwbl_dirtied_after(iwbl, *work->older_than_this))
			break;
		list_move(&iwbl->dirty_list, &tmp);
		moved++;
		if (sb_is_blkdev_sb(inode->i_sb))
			continue;
		if (sb && sb != inode->i_sb)
			do_sb_sort = 1;
		sb = inode->i_sb;
	}

	/* just one sb in list, splice to dispatch_queue and we're done */
	if (!do_sb_sort) {
		list_splice(&tmp, dispatch_queue);
		goto out;
	}

	/* Move inodes from one superblock together */
	while (!list_empty(&tmp)) {
		sb = iwbl_to_inode(dirty_list_to_iwbl(tmp.prev))->i_sb;
		list_for_each_prev_safe(pos, node, &tmp) {
			iwbl = dirty_list_to_iwbl(pos);
			inode = iwbl_to_inode(iwbl);
			if (inode->i_sb == sb)
				list_move(&iwbl->dirty_list, dispatch_queue);
		}
	}
out:
	return moved;
}

/*
 * Queue all expired dirty inodes for io, eldest first.
 * Before
 *         newly dirtied     b_dirty    b_io    b_more_io
 *         =============>    gf         edc     BA
 * After
 *         newly dirtied     b_dirty    b_io    b_more_io
 *         =============>    g          fBAedc
 *                                           |
 *                                           +--> dequeue for IO
 */
static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
{
	int moved;
	assert_spin_locked(&wb->list_lock);
	list_splice_init(&wb->b_more_io, &wb->b_io);
	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
	trace_writeback_queue_io(wb, work, moved);
}

static int write_inode(struct inode *inode, struct writeback_control *wbc)
{
	int ret;

	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
		trace_writeback_write_inode_start(inode, wbc);
		ret = inode->i_sb->s_op->write_inode(inode, wbc);
		trace_writeback_write_inode(inode, wbc);
		return ret;
	}
	return 0;
}

/*
 * Wait for writeback on an inode to complete. Caller must have inode pinned.
 */
void inode_wait_for_writeback(struct inode *inode)
{
	spin_lock(&inode->i_lock);
	__inode_wait_for_writeback(inode);
	spin_unlock(&inode->i_lock);
}

/*
 * Find proper writeback list for the inode depending on its current state and
 * possibly also change of its state while we were doing writeback.  Here we
 * handle things such as livelock prevention or fairness of writeback among
 * inodes. This function can be called only by flusher thread - noone else
 * processes all inodes in writeback lists and requeueing inodes behind flusher
 * thread's back can have unexpected consequences.
 */
static void requeue_inode(struct inode_wb_link *iwbl, struct bdi_writeback *wb,
			  struct writeback_control *wbc)
{
	struct inode *inode = iwbl_to_inode(iwbl);

	if (inode->i_state & I_FREEING)
		return;

	/*
	 * Sync livelock prevention. Each inode is tagged and synced in one
	 * shot. If still dirty, it will be redirty_tail()'ed below.  Update
	 * the dirty time to prevent enqueue and sync it again.
	 */
	if ((inode->i_state & I_DIRTY) &&
	    (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
		iwbl->dirtied_when = jiffies;

	if (wbc->pages_skipped) {
		/*
		 * writeback is not making progress due to locked
		 * buffers. Skip this inode for now.
		 */
		redirty_tail(iwbl, wb);
		return;
	}

	if (iwbl_still_has_dirty_pages(iwbl, inode)) {
		/*
		 * We didn't write back all the pages.  nfs_writepages()
		 * sometimes bales out without doing anything.
		 */
		if (wbc->nr_to_write <= 0) {
			/* Slice used up. Queue for next turn. */
			requeue_io(iwbl, wb);
		} else {
			/*
			 * Writeback blocked by something other than
			 * congestion. Delay the inode for some time to
			 * avoid spinning on the CPU (100% iowait)
			 * retrying writeback of the dirty page/inode
			 * that cannot be performed immediately.
			 */
			redirty_tail(iwbl, wb);
		}
	} else if (iwbl_is_root(iwbl) &&
		   (inode->i_state & (I_DIRTY_SYNC | I_DIRTY_DATASYNC))) {
		/*
		 * Filesystems can dirty the inode during writeback operations,
		 * such as delayed allocation during submission or metadata
		 * updates after data IO completion.
		 */
		redirty_tail(iwbl, wb);
	} else {
		/* The inode is clean. Remove from writeback lists. */
		iwbl_del_locked(iwbl, wb);
	}
}

/*
 * Write out an inode and its dirty pages. Do not update the writeback list
 * linkage. That is left to the caller. The caller is also responsible for
 * setting I_SYNC flag and calling iwbl_sync_complete() to clear it.
 */
static int
__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
{
	struct address_space *mapping = inode->i_mapping;
	struct inode_wb_link *iwbl = inode_writeback_iwbl(inode, wbc);
	long nr_to_write = wbc->nr_to_write;
	bool skip_metadata = wbc_skip_metadata(wbc);
	unsigned dirty;
	int ret;

	WARN_ON(!iwbl_test_sync(iwbl));

	trace_writeback_single_inode_start(inode, wbc, nr_to_write);

	ret = do_writepages(mapping, wbc);

	/*
	 * Make sure to wait on the data before writing out the metadata.
	 * This is important for filesystems that modify metadata on data
	 * I/O completion. We don't do it for sync(2) writeback because it has a
	 * separate, external IO completion path and ->sync_fs for guaranteeing
	 * inode metadata is written back correctly.
	 */
	if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync && !skip_metadata) {
		int err = filemap_fdatawait(mapping);
		if (ret == 0)
			ret = err;
	}

	/*
	 * Some filesystems may redirty the inode during the writeback
	 * due to delalloc, clear dirty metadata flags right before
	 * write_inode()
	 */
	spin_lock(&inode->i_lock);

	if (skip_metadata)
		dirty = inode->i_state & I_DIRTY_PAGES;
	else
		dirty = inode->i_state & I_DIRTY;

	inode->i_state &= ~dirty;

	/*
	 * Paired with smp_mb() in __mark_inode_dirty_dctx().  This allows
	 * the function to perform iwbl_has_enough_dirty() test without
	 * grabbing i_lock - either they see the dirty bits cleared or we
	 * see the dirtied inode.
	 *
	 * I_DIRTY_PAGES is always cleared together above even if @mapping
	 * still has dirty pages.  The flag is reinstated after smp_mb() if
	 * necessary to guarantee that either __mark_inode_dirty_dctx()
	 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
	 */
	smp_mb();

	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
		inode->i_state |= I_DIRTY_PAGES;

	spin_unlock(&inode->i_lock);

	/* Don't write the inode if only I_DIRTY_PAGES was set */
	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
		int err = write_inode(inode, wbc);
		if (ret == 0)
			ret = err;
	}
	trace_writeback_single_inode(inode, wbc, nr_to_write);
	return ret;
}

/*
 * Write out an inode's dirty pages. Either the caller has an active reference
 * on the inode or the inode has I_WILL_FREE set.
 *
 * This function is designed to be called for writing back one inode which
 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
 * and does more profound writeback list handling in writeback_sb_inodes().
 */
static int
writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
{
	struct inode_wb_link *iwbl = inode_writeback_iwbl(inode, wbc);
	struct bdi_writeback *wb = iwbl_to_wb(iwbl);
	int ret = 0;

	spin_lock(&inode->i_lock);
	if (!atomic_read(&inode->i_count))
		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
	else
		WARN_ON(inode->i_state & I_WILL_FREE);

	if (iwbl_test_sync(iwbl)) {
		if (wbc->sync_mode != WB_SYNC_ALL)
			goto out;
		/*
		 * It's a data-integrity sync. We must wait. Since callers hold
		 * inode reference or inode has I_WILL_FREE set, it cannot go
		 * away under us.
		 */
		iwbl_wait_for_writeback(iwbl);
	}
	WARN_ON(iwbl_test_sync(iwbl));
	/*
	 * Skip inode if it is clean and we have no outstanding writeback in
	 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
	 * function since flusher thread may be doing for example sync in
	 * parallel and if we move the inode, it could get skipped. So here we
	 * make sure inode is on some writeback list and leave it there unless
	 * we have completely cleaned the inode.
	 */
	if (!(inode->i_state & I_DIRTY) &&
	    (wbc->sync_mode != WB_SYNC_ALL ||
	     !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
		goto out;
	iwbl_set_sync(iwbl, inode);
	spin_unlock(&inode->i_lock);

	ret = __writeback_single_inode(inode, wbc);

	spin_lock(&wb->list_lock);
	spin_lock(&inode->i_lock);
	/*
	 * If inode is clean, remove it from writeback lists. Otherwise don't
	 * touch it. See comment above for explanation.
	 */
	if (!(inode->i_state & I_DIRTY))
		iwbl_del_locked(iwbl, wb);
	spin_unlock(&wb->list_lock);
	iwbl_sync_complete(iwbl);
out:
	spin_unlock(&inode->i_lock);
	return ret;
}

static long writeback_chunk_size(struct bdi_writeback *wb,
				 struct wb_writeback_work *work)
{
	long pages;

	/*
	 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
	 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
	 * here avoids calling into writeback_inodes_wb() more than once.
	 *
	 * The intended call sequence for WB_SYNC_ALL writeback is:
	 *
	 *      wb_writeback()
	 *          writeback_sb_inodes()       <== called only once
	 *              write_cache_pages()     <== called once for each inode
	 *                   (quickly) tag currently dirty pages
	 *                   (maybe slowly) sync all tagged pages
	 */
	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
		pages = LONG_MAX;
	else {
		pages = min(wb->avg_write_bandwidth / 2,
			    global_dirty_limit / DIRTY_SCOPE);
		pages = min(pages, work->nr_pages);
		pages = round_down(pages + MIN_WRITEBACK_PAGES,
				   MIN_WRITEBACK_PAGES);
	}

	return pages;
}

/*
 * Write a portion of b_io inodes which belong to @sb.
 *
 * Return the number of pages and/or inodes written.
 */
static long writeback_sb_inodes(struct super_block *sb,
				struct bdi_writeback *wb,
				struct wb_writeback_work *work)
{
	struct writeback_control wbc = {
		.sync_mode		= work->sync_mode,
		.tagged_writepages	= work->tagged_writepages,
		.for_kupdate		= work->for_kupdate,
		.for_background		= work->for_background,
		.for_sync		= work->for_sync,
		.range_cyclic		= work->range_cyclic,
		.range_start		= 0,
		.range_end		= LLONG_MAX,
	};
	unsigned long start_time = jiffies;
	long write_chunk;
	long wrote = 0;  /* count both pages and inodes */

	while (!list_empty(&wb->b_io)) {
		struct inode_wb_link *iwbl = dirty_list_to_iwbl(wb->b_io.prev);
		struct inode *inode = iwbl_to_inode(iwbl);

		if (inode->i_sb != sb) {
			if (work->sb) {
				/*
				 * We only want to write back data for this
				 * superblock, move all inodes not belonging
				 * to it back onto the dirty list.
				 */
				redirty_tail(iwbl, wb);
				continue;
			}

			/*
			 * The inode belongs to a different superblock.
			 * Bounce back to the caller to unpin this and
			 * pin the next superblock.
			 */
			break;
		}

		wbc_set_iwbl(&wbc, iwbl);

		/*
		 * Don't bother with new inodes or inodes being freed, first
		 * kind does not need periodic writeout yet, and for the latter
		 * kind writeout is handled by the freer.
		 */
		spin_lock(&inode->i_lock);
		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
			spin_unlock(&inode->i_lock);
			redirty_tail(iwbl, wb);
			continue;
		}
		if (iwbl_test_sync(iwbl) && wbc.sync_mode != WB_SYNC_ALL) {
			/*
			 * If this inode is locked for writeback and we are not
			 * doing writeback-for-data-integrity, move it to
			 * b_more_io so that writeback can proceed with the
			 * other inodes on s_io.
			 *
			 * We'll have another go at writing back this inode
			 * when we completed a full scan of b_io.
			 */
			spin_unlock(&inode->i_lock);
			requeue_io(iwbl, wb);
			trace_writeback_sb_inodes_requeue(inode);
			continue;
		}
		spin_unlock(&wb->list_lock);

		/*
		 * We already requeued the inode if it had I_SYNC set and we
		 * are doing WB_SYNC_NONE writeback. So this catches only the
		 * WB_SYNC_ALL case.
		 */
		if (iwbl_test_sync(iwbl)) {
			/* Wait for I_SYNC. This function drops i_lock... */
			iwbl_sleep_on_writeback(iwbl);
			/* Inode may be gone, start again */
			spin_lock(&wb->list_lock);
			continue;
		}
		iwbl_set_sync(iwbl, inode);
		spin_unlock(&inode->i_lock);

		write_chunk = writeback_chunk_size(wb, work);
		wbc.nr_to_write = write_chunk;
		wbc.pages_skipped = 0;

		/*
		 * We use I_SYNC to pin the inode in memory. While it is set
		 * evict_inode() will wait so the inode cannot be freed.
		 */
		__writeback_single_inode(inode, &wbc);

		work->nr_pages -= write_chunk - wbc.nr_to_write;
		wrote += write_chunk - wbc.nr_to_write;
		spin_lock(&wb->list_lock);
		spin_lock(&inode->i_lock);
		if (!(inode->i_state & I_DIRTY))
			wrote++;
		requeue_inode(iwbl, wb, &wbc);
		iwbl_sync_complete(iwbl);
		spin_unlock(&inode->i_lock);
		cond_resched_lock(&wb->list_lock);
		/*
		 * bail out to wb_writeback() often enough to check
		 * background threshold and other termination conditions.
		 */
		if (wrote) {
			if (time_is_before_jiffies(start_time + HZ / 10UL))
				break;
			if (work->nr_pages <= 0)
				break;
		}
	}
	return wrote;
}

static long __writeback_inodes_wb(struct bdi_writeback *wb,
				  struct wb_writeback_work *work)
{
	unsigned long start_time = jiffies;
	long wrote = 0;

	while (!list_empty(&wb->b_io)) {
		struct inode_wb_link *iwbl = dirty_list_to_iwbl(wb->b_io.prev);
		struct inode *inode = iwbl_to_inode(iwbl);
		struct super_block *sb = inode->i_sb;

		if (!grab_super_passive(sb)) {
			/*
			 * grab_super_passive() may fail consistently due to
			 * s_umount being grabbed by someone else. Don't use
			 * requeue_io() to avoid busy retrying the inode/sb.
			 */
			redirty_tail(iwbl, wb);
			continue;
		}
		wrote += writeback_sb_inodes(sb, wb, work);
		drop_super(sb);

		/* refer to the same tests at the end of writeback_sb_inodes */
		if (wrote) {
			if (time_is_before_jiffies(start_time + HZ / 10UL))
				break;
			if (work->nr_pages <= 0)
				break;
		}
	}
	/* Leave any unwritten inodes on b_io */
	return wrote;
}

static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
				enum wb_reason reason)
{
	struct wb_writeback_work work = {
		.nr_pages	= nr_pages,
		.sync_mode	= WB_SYNC_NONE,
		.range_cyclic	= 1,
		.reason		= reason,
	};

	spin_lock(&wb->list_lock);
	if (list_empty(&wb->b_io))
		queue_io(wb, &work);
	__writeback_inodes_wb(wb, &work);
	spin_unlock(&wb->list_lock);

	return nr_pages - work.nr_pages;
}

static bool over_bground_thresh(struct bdi_writeback *wb)
{
	unsigned long background_thresh, dirty_thresh;

	global_dirty_limits(&background_thresh, &dirty_thresh);

	if (global_page_state(NR_FILE_DIRTY) +
	    global_page_state(NR_UNSTABLE_NFS) > background_thresh)
		return true;

	if (wb_stat(wb, WB_RECLAIMABLE) > wb_dirty_limit(wb, background_thresh))
		return true;

	return false;
}

/*
 * Called under wb->list_lock. If there are multiple wb per bdi,
 * only the flusher working on the first wb should do it.
 */
static void wb_update_bandwidth(struct bdi_writeback *wb,
				unsigned long start_time)
{
	__wb_update_bandwidth(wb, 0, 0, 0, 0, 0, start_time);
}

/*
 * Explicit flushing or periodic writeback of "old" data.
 *
 * Define "old": the first time one of an inode's pages is dirtied, we mark the
 * dirtying-time in the inode's address_space.  So this periodic writeback code
 * just walks the superblock inode list, writing back any inodes which are
 * older than a specific point in time.
 *
 * Try to run once per dirty_writeback_interval.  But if a writeback event
 * takes longer than a dirty_writeback_interval interval, then leave a
 * one-second gap.
 *
 * older_than_this takes precedence over nr_to_write.  So we'll only write back
 * all dirty pages if they are all attached to "old" mappings.
 */
static long wb_writeback(struct bdi_writeback *wb,
			 struct wb_writeback_work *work)
{
	unsigned long wb_start = jiffies;
	long nr_pages = work->nr_pages;
	unsigned long oldest_jif;
	struct inode_wb_link *iwbl;
	struct inode *inode;
	long progress;

	oldest_jif = jiffies;
	work->older_than_this = &oldest_jif;

	spin_lock(&wb->list_lock);
	for (;;) {
		/*
		 * Stop writeback when nr_pages has been consumed
		 */
		if (work->nr_pages <= 0)
			break;

		/*
		 * Background writeout and kupdate-style writeback may
		 * run forever. Stop them if there is other work to do
		 * so that e.g. sync can proceed. They'll be restarted
		 * after the other works are all done.
		 */
		if ((work->for_background || work->for_kupdate) &&
		    !list_empty(&wb->work_list))
			break;

		/*
		 * For background writeout, stop when we are below the
		 * background dirty threshold
		 */
		if (work->for_background && !over_bground_thresh(wb))
			break;

		/*
		 * Kupdate and background works are special and we want to
		 * include all inodes that need writing. Livelock avoidance is
		 * handled by these works yielding to any other work so we are
		 * safe.
		 */
		if (work->for_kupdate) {
			oldest_jif = jiffies -
				msecs_to_jiffies(dirty_expire_interval * 10);
		} else if (work->for_background)
			oldest_jif = jiffies;

		trace_writeback_start(wb->bdi, work);
		if (list_empty(&wb->b_io))
			queue_io(wb, work);
		if (work->sb)
			progress = writeback_sb_inodes(work->sb, wb, work);
		else
			progress = __writeback_inodes_wb(wb, work);
		trace_writeback_written(wb->bdi, work);

		wb_update_bandwidth(wb, wb_start);

		/*
		 * Did we write something? Try for more
		 *
		 * Dirty inodes are moved to b_io for writeback in batches.
		 * The completion of the current batch does not necessarily
		 * mean the overall work is done. So we keep looping as long
		 * as made some progress on cleaning pages or inodes.
		 */
		if (progress)
			continue;
		/*
		 * No more inodes for IO, bail
		 */
		if (list_empty(&wb->b_more_io))
			break;
		/*
		 * Nothing written. Wait for some inode to
		 * become available for writeback. Otherwise
		 * we'll just busyloop.
		 */
		if (!list_empty(&wb->b_more_io))  {
			trace_writeback_wait(wb->bdi, work);
			iwbl = dirty_list_to_iwbl(wb->b_more_io.prev);
			inode = iwbl_to_inode(iwbl);
			spin_lock(&inode->i_lock);
			spin_unlock(&wb->list_lock);
			/* This function drops i_lock... */
			iwbl_sleep_on_writeback(iwbl);
			spin_lock(&wb->list_lock);
		}
	}
	spin_unlock(&wb->list_lock);

	return nr_pages - work->nr_pages;
}

/*
 * Return the next wb_writeback_work struct that hasn't been processed yet.
 */
static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
{
	struct wb_writeback_work *work = NULL;

	spin_lock_bh(&wb->work_lock);
	if (!list_empty(&wb->work_list)) {
		work = list_entry(wb->work_list.next,
				  struct wb_writeback_work, list);
		list_del_init(&work->list);
	}
	spin_unlock_bh(&wb->work_lock);
	return work;
}

/*
 * Add in the number of potentially dirty inodes, because each inode
 * write can dirty pagecache in the underlying blockdev.
 */
static unsigned long get_nr_dirty_pages(void)
{
	return global_page_state(NR_FILE_DIRTY) +
		global_page_state(NR_UNSTABLE_NFS) +
		get_nr_dirty_inodes();
}

static long wb_check_background_flush(struct bdi_writeback *wb)
{
	if (over_bground_thresh(wb)) {

		struct wb_writeback_work work = {
			.nr_pages	= LONG_MAX,
			.sync_mode	= WB_SYNC_NONE,
			.for_background	= 1,
			.range_cyclic	= 1,
			.reason		= WB_REASON_BACKGROUND,
		};

		return wb_writeback(wb, &work);
	}

	return 0;
}

static long wb_check_old_data_flush(struct bdi_writeback *wb)
{
	unsigned long expired;
	long nr_pages;

	/*
	 * When set to zero, disable periodic writeback
	 */
	if (!dirty_writeback_interval)
		return 0;

	expired = wb->last_old_flush +
			msecs_to_jiffies(dirty_writeback_interval * 10);
	if (time_before(jiffies, expired))
		return 0;

	wb->last_old_flush = jiffies;
	nr_pages = get_nr_dirty_pages();

	if (nr_pages) {
		struct wb_writeback_work work = {
			.nr_pages	= nr_pages,
			.sync_mode	= WB_SYNC_NONE,
			.for_kupdate	= 1,
			.range_cyclic	= 1,
			.reason		= WB_REASON_PERIODIC,
		};

		return wb_writeback(wb, &work);
	}

	return 0;
}

/*
 * Retrieve work items and do the writeback they describe
 */
static long wb_do_writeback(struct bdi_writeback *wb)
{
	struct wb_writeback_work *work;
	long wrote = 0;

	set_bit(WB_writeback_running, &wb->state);
	while ((work = get_next_work_item(wb)) != NULL) {
		struct wb_completion *done = work->done;
		bool need_wake_up = false;

		trace_writeback_exec(wb->bdi, work);

		if (!maybe_writeback_single_mapping(work))
			wrote += wb_writeback(wb, work);

		if (work->single_wait) {
			WARN_ON_ONCE(work->auto_free);
			/* paired w/ rmb in wb_wait_for_single_work() */
			smp_wmb();
			work->single_done = 1;
			need_wake_up = true;
		} else if (work->auto_free) {
			kfree(work);
		}

		if (done && atomic_dec_and_test(&done->cnt))
			need_wake_up = true;

		if (need_wake_up)
			wake_up_all(&wb->bdi->wb_waitq);
	}

	/*
	 * Check for periodic writeback, kupdated() style
	 */
	wrote += wb_check_old_data_flush(wb);
	wrote += wb_check_background_flush(wb);
	clear_bit(WB_writeback_running, &wb->state);

	return wrote;
}

/*
 * Handle writeback of dirty data for the device backed by this bdi. Also
 * reschedules periodically and does kupdated style flushing.
 */
void wb_workfn(struct work_struct *work)
{
	struct bdi_writeback *wb = container_of(to_delayed_work(work),
						struct bdi_writeback, dwork);
	long pages_written;

	set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
	current->flags |= PF_SWAPWRITE;

	if (likely(!current_is_workqueue_rescuer() ||
		   !test_bit(WB_registered, &wb->state))) {
		/*
		 * The normal path.  Keep writing back @wb until its
		 * work_list is empty.  Note that this path is also taken
		 * if @wb is shutting down even when we're running off the
		 * rescuer as work_list needs to be drained.
		 */
		do {
			pages_written = wb_do_writeback(wb);
			trace_writeback_pages_written(pages_written);
		} while (!list_empty(&wb->work_list));
	} else {
		/*
		 * bdi_wq can't get enough workers and we're running off
		 * the emergency worker.  Don't hog it.  Hopefully, 1024 is
		 * enough for efficient IO.
		 */
		pages_written = writeback_inodes_wb(wb, 1024,
						    WB_REASON_FORKER_THREAD);
		trace_writeback_pages_written(pages_written);
	}

	if (!list_empty(&wb->work_list))
		mod_delayed_work(bdi_wq, &wb->dwork, 0);
	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
		wb_wakeup_delayed(wb);

	current->flags &= ~PF_SWAPWRITE;
}

/*
 * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
 * the whole world.
 */
void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
{
	struct backing_dev_info *bdi;

	if (!nr_pages)
		nr_pages = get_nr_dirty_pages();

	rcu_read_lock();
	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
		struct bdi_writeback *wb;
		struct wb_iter iter;

		if (!bdi_has_dirty_io(bdi))
			continue;

		bdi_for_each_wb(wb, bdi, &iter, 0)
			wb_start_writeback(wb, wb_split_bdi_pages(wb, nr_pages),
					   false, reason);
	}
	rcu_read_unlock();
}

static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
	if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
		struct dentry *dentry;
		const char *name = "?";

		dentry = d_find_alias(inode);
		if (dentry) {
			spin_lock(&dentry->d_lock);
			name = (const char *) dentry->d_name.name;
		}
		printk(KERN_DEBUG
		       "%s(%d): dirtied inode %lu (%s) on %s\n",
		       current->comm, task_pid_nr(current), inode->i_ino,
		       name, inode->i_sb->s_id);
		if (dentry) {
			spin_unlock(&dentry->d_lock);
			dput(dentry);
		}
	}
}

static void __mark_inode_dirty_dctx(struct dirty_context *dctx, int flags)
{
	struct inode *inode = dctx->inode;
	struct inode_wb_link *iwbl = dctx->iwbl;
	struct bdi_writeback *wb = dctx->wb;
	struct super_block *sb = inode->i_sb;

	/*
	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
	 * dirty the inode itself
	 */
	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
		trace_writeback_dirty_inode_start(inode, flags);

		if (sb->s_op->dirty_inode)
			sb->s_op->dirty_inode(inode, flags);

		trace_writeback_dirty_inode(inode, flags);
	}

	/*
	 * Paired with smp_mb()'s in __writeback_single_inode() and
	 * mapping_writeback_maybe_whole() for the following lockless
	 * iwbl_has_enough_dirty() test.  See there for details.
	 */
	smp_mb();

	if (iwbl_has_enough_dirty(iwbl, inode, flags))
		return;

	if (unlikely(block_dump))
		block_dump___mark_inode_dirty(inode);

	spin_lock(&inode->i_lock);
	if (!iwbl_has_enough_dirty(iwbl, inode, flags)) {
		bool was_dirty;

		was_dirty = iwbl_set_dirty(iwbl, inode, flags);

		/*
		 * If the inode is being synced, just update its dirty state.
		 * The unlocker will place the inode on the appropriate
		 * superblock list, based upon its state.
		 */
		if (iwbl_test_sync(iwbl))
			goto out_unlock_inode;

		/*
		 * Only add valid (hashed) inodes to the superblock's
		 * dirty list.  Add blockdev inodes as well.
		 */
		if (!S_ISBLK(inode->i_mode)) {
			if (inode_unhashed(inode))
				goto out_unlock_inode;
		}
		if (inode->i_state & I_FREEING)
			goto out_unlock_inode;

		/*
		 * If the inode was already on b_dirty/b_io/b_more_io, don't
		 * reposition it (that would break b_dirty time-ordering).
		 */
		if (!was_dirty) {
			bool wakeup_bdi = false;

			spin_unlock(&inode->i_lock);
			spin_lock(&wb->list_lock);

			WARN(bdi_cap_writeback_dirty(wb->bdi) &&
			     !test_bit(WB_registered, &wb->state),
			     "bdi-%s not registered\n", wb->bdi->name);

			iwbl->dirtied_when = jiffies;
			wakeup_bdi = iwbl_move_locked(iwbl, wb, &wb->b_dirty);
			spin_unlock(&wb->list_lock);

			/*
			 * If this is the first dirty inode for this bdi,
			 * we have to wake-up the corresponding bdi thread
			 * to make sure background write-back happens
			 * later.
			 */
			if (bdi_cap_writeback_dirty(wb->bdi) && wakeup_bdi)
				wb_wakeup_delayed(wb);
			return;
		}
	}
out_unlock_inode:
	spin_unlock(&inode->i_lock);

}
EXPORT_SYMBOL(mark_inode_dirty_dctx);

/**
 *	mark_inode_dirty_dctx -	internal function
 *	@dctx: dirty_context containing the target inode
 *	@flags: what kind of dirty (i.e. I_DIRTY_SYNC)
 *	Mark an inode as dirty. Callers should use mark_inode_dirty or
 *  	mark_inode_dirty_sync.
 *
 * Put the inode on the super block's dirty list.
 *
 * CAREFUL! We mark it dirty unconditionally, but move it onto the
 * dirty list only if it is hashed or if it refers to a blockdev.
 * If it was not hashed, it will never be added to the dirty list
 * even if it is later hashed, as it will have been marked dirty already.
 *
 * In short, make sure you hash any inodes _before_ you start marking
 * them dirty.
 *
 * Note that for blockdevs, iwbl->dirtied_when represents the dirtying time of
 * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
 * the kernel-internal blockdev inode represents the dirtying time of the
 * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
 * page->mapping->host, so the page-dirtying time is recorded in the internal
 * blockdev inode.
 */
void mark_inode_dirty_dctx(struct dirty_context *dctx, int flags)
{
	/*
	 * I_DIRTY_PAGES should dirty @dctx->iwbl but I_DIRTY_[DATA]SYNC
	 * should always dirty the root iwbl.  If @dctx->iwbl is root, we
	 * can do both at the same time; otherwise, handle the two dirtying
	 * separately.
	 */
	if (iwbl_is_root(dctx->iwbl) ||
	    !(flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC))) {
		__mark_inode_dirty_dctx(dctx, flags);
		return;
	}

	if (flags & I_DIRTY_PAGES)
		__mark_inode_dirty_dctx(dctx, I_DIRTY_PAGES);

	flags &= ~I_DIRTY_PAGES;
	if (flags)
		__mark_inode_dirty(dctx->inode, flags);
}

void __mark_inode_dirty(struct inode *inode, int flags)
{
	struct dirty_context dctx;

	init_dirty_inode_context(&dctx, inode);
	mark_inode_dirty_dctx(&dctx, flags);
}
EXPORT_SYMBOL(__mark_inode_dirty);

static void wait_sb_inodes(struct super_block *sb)
{
	struct inode *inode, *old_inode = NULL;

	/*
	 * We need to be protected against the filesystem going from
	 * r/o to r/w or vice versa.
	 */
	WARN_ON(!rwsem_is_locked(&sb->s_umount));

	spin_lock(&inode_sb_list_lock);

	/*
	 * Data integrity sync. Must wait for all pages under writeback,
	 * because there may have been pages dirtied before our sync
	 * call, but which had writeout started before we write it out.
	 * In which case, the inode may not be on the dirty list, but
	 * we still have to wait for that writeout.
	 */
	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
		struct address_space *mapping = inode->i_mapping;

		spin_lock(&inode->i_lock);
		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
		    (mapping->nrpages == 0)) {
			spin_unlock(&inode->i_lock);
			continue;
		}
		__iget(inode);
		spin_unlock(&inode->i_lock);
		spin_unlock(&inode_sb_list_lock);

		/*
		 * We hold a reference to 'inode' so it couldn't have been
		 * removed from s_inodes list while we dropped the
		 * inode_sb_list_lock.  We cannot iput the inode now as we can
		 * be holding the last reference and we cannot iput it under
		 * inode_sb_list_lock. So we keep the reference and iput it
		 * later.
		 */
		iput(old_inode);
		old_inode = inode;

		filemap_fdatawait(mapping);

		cond_resched();

		spin_lock(&inode_sb_list_lock);
	}
	spin_unlock(&inode_sb_list_lock);
	iput(old_inode);
}

static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
				     enum wb_reason reason, bool skip_if_busy)
{
	DEFINE_WB_COMPLETION_ONSTACK(done);
	struct wb_writeback_work work = {
		.sb			= sb,
		.sync_mode		= WB_SYNC_NONE,
		.tagged_writepages	= 1,
		.done			= &done,
		.nr_pages		= nr,
		.reason			= reason,
	};
	struct backing_dev_info *bdi = sb->s_bdi;

	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
		return;
	WARN_ON(!rwsem_is_locked(&sb->s_umount));

	bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
	wb_wait_for_completion(bdi, &done);
}

/**
 * writeback_inodes_sb_nr -	writeback dirty inodes from given super_block
 * @sb: the superblock
 * @nr: the number of pages to write
 * @reason: reason why some writeback work initiated
 *
 * Start writeback on some inodes on this super_block. No guarantees are made
 * on how many (if any) will be written, and this function does not wait
 * for IO completion of submitted IO.
 */
void writeback_inodes_sb_nr(struct super_block *sb,
			    unsigned long nr,
			    enum wb_reason reason)
{
	__writeback_inodes_sb_nr(sb, nr, reason, false);
}
EXPORT_SYMBOL(writeback_inodes_sb_nr);

/**
 * writeback_inodes_sb	-	writeback dirty inodes from given super_block
 * @sb: the superblock
 * @reason: reason why some writeback work was initiated
 *
 * Start writeback on some inodes on this super_block. No guarantees are made
 * on how many (if any) will be written, and this function does not wait
 * for IO completion of submitted IO.
 */
void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(writeback_inodes_sb);

/**
 * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
 * @sb: the superblock
 * @nr: the number of pages to write
 * @reason: the reason of writeback
 *
 * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
 * Returns 1 if writeback was started, 0 if not.
 */
bool try_to_writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
				   enum wb_reason reason)
{
	if (!down_read_trylock(&sb->s_umount))
		return false;

	__writeback_inodes_sb_nr(sb, nr, reason, true);
	up_read(&sb->s_umount);
	return true;
}
EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);

/**
 * try_to_writeback_inodes_sb - try to start writeback if none underway
 * @sb: the superblock
 * @reason: reason why some writeback work was initiated
 *
 * Implement by try_to_writeback_inodes_sb_nr()
 * Returns 1 if writeback was started, 0 if not.
 */
bool try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
	return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(try_to_writeback_inodes_sb);

/**
 * sync_inodes_sb	-	sync sb inode pages
 * @sb: the superblock
 *
 * This function writes and waits on any dirty inode belonging to this
 * super_block.
 */
void sync_inodes_sb(struct super_block *sb)
{
	DEFINE_WB_COMPLETION_ONSTACK(done);
	struct wb_writeback_work work = {
		.sb		= sb,
		.sync_mode	= WB_SYNC_ALL,
		.nr_pages	= LONG_MAX,
		.range_cyclic	= 0,
		.done		= &done,
		.reason		= WB_REASON_SYNC,
		.for_sync	= 1,
	};
	struct backing_dev_info *bdi = sb->s_bdi;

	/* Nothing to do? */
	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
		return;
	WARN_ON(!rwsem_is_locked(&sb->s_umount));

	bdi_split_work_to_wbs(bdi, &work, false);
	wb_wait_for_completion(bdi, &done);

	wait_sb_inodes(sb);
}
EXPORT_SYMBOL(sync_inodes_sb);

/**
 * write_inode_now	-	write an inode to disk
 * @inode: inode to write to disk
 * @sync: whether the write should be synchronous or not
 *
 * This function commits an inode to disk immediately if it is dirty. This is
 * primarily needed by knfsd.
 *
 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
 */
int write_inode_now(struct inode *inode, int sync)
{
	struct writeback_control wbc = {
		.nr_to_write = LONG_MAX,
		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
		.range_start = 0,
		.range_end = LLONG_MAX,
	};

	if (!mapping_cap_writeback_dirty(inode->i_mapping))
		wbc.nr_to_write = 0;

	might_sleep();
	return writeback_single_inode(inode, &wbc);
}
EXPORT_SYMBOL(write_inode_now);

/**
 * sync_inode - write an inode and its pages to disk.
 * @inode: the inode to sync
 * @wbc: controls the writeback mode
 *
 * sync_inode() will write an inode and its pages to disk.  It will also
 * correctly update the inode on its superblock's dirty inode lists and will
 * update inode->i_state.
 *
 * The caller must have a ref on the inode.
 */
int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
	return writeback_single_inode(inode, wbc);
}
EXPORT_SYMBOL(sync_inode);

/**
 * sync_inode_metadata - write an inode to disk
 * @inode: the inode to sync
 * @wait: wait for I/O to complete.
 *
 * Write an inode to disk and adjust its dirty state after completion.
 *
 * Note: only writes the actual inode, no associated data or other metadata.
 */
int sync_inode_metadata(struct inode *inode, int wait)
{
	struct writeback_control wbc = {
		.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
		.nr_to_write = 0, /* metadata-only */
	};

	return sync_inode(inode, &wbc);
}
EXPORT_SYMBOL(sync_inode_metadata);