blob: db578783dd36a3efc87b2bd052ba1353438850ed [file] [log] [blame]
/*
* kernel/locking/mutex.c
*
* Mutexes: blocking mutual exclusion locks
*
* Started by Ingo Molnar:
*
* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*
* Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
* David Howells for suggestions and improvements.
*
* - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
* from the -rt tree, where it was originally implemented for rtmutexes
* by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
* and Sven Dietrich.
*
* Also see Documentation/locking/mutex-design.txt.
*/
#include <linux/mutex.h>
#include <linux/ww_mutex.h>
#include <linux/sched/signal.h>
#include <linux/sched/rt.h>
#include <linux/sched/wake_q.h>
#include <linux/sched/debug.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/debug_locks.h>
#include <linux/osq_lock.h>
#ifdef CONFIG_DEBUG_MUTEXES
# include "mutex-debug.h"
#else
# include "mutex.h"
#endif
void
__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
{
atomic_long_set(&lock->owner, 0);
spin_lock_init(&lock->wait_lock);
INIT_LIST_HEAD(&lock->wait_list);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
osq_lock_init(&lock->osq);
#endif
debug_mutex_init(lock, name, key);
}
EXPORT_SYMBOL(__mutex_init);
/*
* @owner: contains: 'struct task_struct *' to the current lock owner,
* NULL means not owned. Since task_struct pointers are aligned at
* at least L1_CACHE_BYTES, we have low bits to store extra state.
*
* Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
* Bit1 indicates unlock needs to hand the lock to the top-waiter
* Bit2 indicates handoff has been done and we're waiting for pickup.
*/
#define MUTEX_FLAG_WAITERS 0x01
#define MUTEX_FLAG_HANDOFF 0x02
#define MUTEX_FLAG_PICKUP 0x04
#define MUTEX_FLAGS 0x07
static inline struct task_struct *__owner_task(unsigned long owner)
{
return (struct task_struct *)(owner & ~MUTEX_FLAGS);
}
static inline unsigned long __owner_flags(unsigned long owner)
{
return owner & MUTEX_FLAGS;
}
/*
* Trylock variant that retuns the owning task on failure.
*/
static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
{
unsigned long owner, curr = (unsigned long)current;
owner = atomic_long_read(&lock->owner);
for (;;) { /* must loop, can race against a flag */
unsigned long old, flags = __owner_flags(owner);
unsigned long task = owner & ~MUTEX_FLAGS;
if (task) {
if (likely(task != curr))
break;
if (likely(!(flags & MUTEX_FLAG_PICKUP)))
break;
flags &= ~MUTEX_FLAG_PICKUP;
} else {
#ifdef CONFIG_DEBUG_MUTEXES
DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
#endif
}
/*
* We set the HANDOFF bit, we must make sure it doesn't live
* past the point where we acquire it. This would be possible
* if we (accidentally) set the bit on an unlocked mutex.
*/
flags &= ~MUTEX_FLAG_HANDOFF;
old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
if (old == owner)
return NULL;
owner = old;
}
return __owner_task(owner);
}
/*
* Actual trylock that will work on any unlocked state.
*/
static inline bool __mutex_trylock(struct mutex *lock)
{
return !__mutex_trylock_or_owner(lock);
}
#ifndef CONFIG_DEBUG_LOCK_ALLOC
/*
* Lockdep annotations are contained to the slow paths for simplicity.
* There is nothing that would stop spreading the lockdep annotations outwards
* except more code.
*/
/*
* Optimistic trylock that only works in the uncontended case. Make sure to
* follow with a __mutex_trylock() before failing.
*/
static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
{
unsigned long curr = (unsigned long)current;
unsigned long zero = 0UL;
if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
return true;
return false;
}
static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
{
unsigned long curr = (unsigned long)current;
if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
return true;
return false;
}
#endif
static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
{
atomic_long_or(flag, &lock->owner);
}
static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
{
atomic_long_andnot(flag, &lock->owner);
}
static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
{
return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
}
/*
* Add @waiter to a given location in the lock wait_list and set the
* FLAG_WAITERS flag if it's the first waiter.
*/
static void __sched
__mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
struct list_head *list)
{
debug_mutex_add_waiter(lock, waiter, current);
list_add_tail(&waiter->list, list);
if (__mutex_waiter_is_first(lock, waiter))
__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
}
/*
* Give up ownership to a specific task, when @task = NULL, this is equivalent
* to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
* WAITERS. Provides RELEASE semantics like a regular unlock, the
* __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
*/
static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
{
unsigned long owner = atomic_long_read(&lock->owner);
for (;;) {
unsigned long old, new;
#ifdef CONFIG_DEBUG_MUTEXES
DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
#endif
new = (owner & MUTEX_FLAG_WAITERS);
new |= (unsigned long)task;
if (task)
new |= MUTEX_FLAG_PICKUP;
old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
if (old == owner)
break;
owner = old;
}
}
#ifndef CONFIG_DEBUG_LOCK_ALLOC
/*
* We split the mutex lock/unlock logic into separate fastpath and
* slowpath functions, to reduce the register pressure on the fastpath.
* We also put the fastpath first in the kernel image, to make sure the
* branch is predicted by the CPU as default-untaken.
*/
static void __sched __mutex_lock_slowpath(struct mutex *lock);
/**
* mutex_lock - acquire the mutex
* @lock: the mutex to be acquired
*
* Lock the mutex exclusively for this task. If the mutex is not
* available right now, it will sleep until it can get it.
*
* The mutex must later on be released by the same task that
* acquired it. Recursive locking is not allowed. The task
* may not exit without first unlocking the mutex. Also, kernel
* memory where the mutex resides must not be freed with
* the mutex still locked. The mutex must first be initialized
* (or statically defined) before it can be locked. memset()-ing
* the mutex to 0 is not allowed.
*
* (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
* checks that will enforce the restrictions and will also do
* deadlock debugging)
*
* This function is similar to (but not equivalent to) down().
*/
void __sched mutex_lock(struct mutex *lock)
{
might_sleep();
if (!__mutex_trylock_fast(lock))
__mutex_lock_slowpath(lock);
}
EXPORT_SYMBOL(mutex_lock);
#endif
/*
* Wait-Die:
* The newer transactions are killed when:
* It (the new transaction) makes a request for a lock being held
* by an older transaction.
*
* Wound-Wait:
* The newer transactions are wounded when:
* An older transaction makes a request for a lock being held by
* the newer transaction.
*/
/*
* Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
* it.
*/
static __always_inline void
ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
{
#ifdef CONFIG_DEBUG_MUTEXES
/*
* If this WARN_ON triggers, you used ww_mutex_lock to acquire,
* but released with a normal mutex_unlock in this call.
*
* This should never happen, always use ww_mutex_unlock.
*/
DEBUG_LOCKS_WARN_ON(ww->ctx);
/*
* Not quite done after calling ww_acquire_done() ?
*/
DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
if (ww_ctx->contending_lock) {
/*
* After -EDEADLK you tried to
* acquire a different ww_mutex? Bad!
*/
DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
/*
* You called ww_mutex_lock after receiving -EDEADLK,
* but 'forgot' to unlock everything else first?
*/
DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
ww_ctx->contending_lock = NULL;
}
/*
* Naughty, using a different class will lead to undefined behavior!
*/
DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
#endif
ww_ctx->acquired++;
ww->ctx = ww_ctx;
}
/*
* Determine if context @a is 'after' context @b. IOW, @a is a younger
* transaction than @b and depending on algorithm either needs to wait for
* @b or die.
*/
static inline bool __sched
__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
{
return (signed long)(a->stamp - b->stamp) > 0;
}
/*
* Wait-Die; wake a younger waiter context (when locks held) such that it can
* die.
*
* Among waiters with context, only the first one can have other locks acquired
* already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
* __ww_mutex_check_kill() wake any but the earliest context.
*/
static bool __sched
__ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
struct ww_acquire_ctx *ww_ctx)
{
if (!ww_ctx->is_wait_die)
return false;
if (waiter->ww_ctx->acquired > 0 &&
__ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
debug_mutex_wake_waiter(lock, waiter);
wake_up_process(waiter->task);
}
return true;
}
/*
* Wound-Wait; wound a younger @hold_ctx if it holds the lock.
*
* Wound the lock holder if there are waiters with older transactions than
* the lock holders. Even if multiple waiters may wound the lock holder,
* it's sufficient that only one does.
*/
static bool __ww_mutex_wound(struct mutex *lock,
struct ww_acquire_ctx *ww_ctx,
struct ww_acquire_ctx *hold_ctx)
{
struct task_struct *owner = __mutex_owner(lock);
lockdep_assert_held(&lock->wait_lock);
/*
* Possible through __ww_mutex_add_waiter() when we race with
* ww_mutex_set_context_fastpath(). In that case we'll get here again
* through __ww_mutex_check_waiters().
*/
if (!hold_ctx)
return false;
/*
* Can have !owner because of __mutex_unlock_slowpath(), but if owner,
* it cannot go away because we'll have FLAG_WAITERS set and hold
* wait_lock.
*/
if (!owner)
return false;
if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
hold_ctx->wounded = 1;
/*
* wake_up_process() paired with set_current_state()
* inserts sufficient barriers to make sure @owner either sees
* it's wounded in __ww_mutex_check_kill() or has a
* wakeup pending to re-read the wounded state.
*/
if (owner != current)
wake_up_process(owner);
return true;
}
return false;
}
/*
* We just acquired @lock under @ww_ctx, if there are later contexts waiting
* behind us on the wait-list, check if they need to die, or wound us.
*
* See __ww_mutex_add_waiter() for the list-order construction; basically the
* list is ordered by stamp, smallest (oldest) first.
*
* This relies on never mixing wait-die/wound-wait on the same wait-list;
* which is currently ensured by that being a ww_class property.
*
* The current task must not be on the wait list.
*/
static void __sched
__ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
{
struct mutex_waiter *cur;
lockdep_assert_held(&lock->wait_lock);
list_for_each_entry(cur, &lock->wait_list, list) {
if (!cur->ww_ctx)
continue;
if (__ww_mutex_die(lock, cur, ww_ctx) ||
__ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
break;
}
}
/*
* After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
* and wake up any waiters so they can recheck.
*/
static __always_inline void
ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
ww_mutex_lock_acquired(lock, ctx);
/*
* The lock->ctx update should be visible on all cores before
* the WAITERS check is done, otherwise contended waiters might be
* missed. The contended waiters will either see ww_ctx == NULL
* and keep spinning, or it will acquire wait_lock, add itself
* to waiter list and sleep.
*/
smp_mb(); /* See comments above and below. */
/*
* [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
* MB MB
* [R] MUTEX_FLAG_WAITERS [R] ww->ctx
*
* The memory barrier above pairs with the memory barrier in
* __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
* and/or !empty list.
*/
if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
return;
/*
* Uh oh, we raced in fastpath, check if any of the waiters need to
* die or wound us.
*/
spin_lock(&lock->base.wait_lock);
__ww_mutex_check_waiters(&lock->base, ctx);
spin_unlock(&lock->base.wait_lock);
}
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
static inline
bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
struct mutex_waiter *waiter)
{
struct ww_mutex *ww;
ww = container_of(lock, struct ww_mutex, base);
/*
* If ww->ctx is set the contents are undefined, only
* by acquiring wait_lock there is a guarantee that
* they are not invalid when reading.
*
* As such, when deadlock detection needs to be
* performed the optimistic spinning cannot be done.
*
* Check this in every inner iteration because we may
* be racing against another thread's ww_mutex_lock.
*/
if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
return false;
/*
* If we aren't on the wait list yet, cancel the spin
* if there are waiters. We want to avoid stealing the
* lock from a waiter with an earlier stamp, since the
* other thread may already own a lock that we also
* need.
*/
if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
return false;
/*
* Similarly, stop spinning if we are no longer the
* first waiter.
*/
if (waiter && !__mutex_waiter_is_first(lock, waiter))
return false;
return true;
}
/*
* Look out! "owner" is an entirely speculative pointer access and not
* reliable.
*
* "noinline" so that this function shows up on perf profiles.
*/
static noinline
bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
{
bool ret = true;
rcu_read_lock();
while (__mutex_owner(lock) == owner) {
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking lock->owner still matches owner. If that fails,
* owner might point to freed memory. If it still matches,
* the rcu_read_lock() ensures the memory stays valid.
*/
barrier();
/*
* Use vcpu_is_preempted to detect lock holder preemption issue.
*/
if (!owner->on_cpu || need_resched() ||
vcpu_is_preempted(task_cpu(owner))) {
ret = false;
break;
}
if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
ret = false;
break;
}
cpu_relax();
}
rcu_read_unlock();
return ret;
}
/*
* Initial check for entering the mutex spinning loop
*/
static inline int mutex_can_spin_on_owner(struct mutex *lock)
{
struct task_struct *owner;
int retval = 1;
if (need_resched())
return 0;
rcu_read_lock();
owner = __mutex_owner(lock);
/*
* As lock holder preemption issue, we both skip spinning if task is not
* on cpu or its cpu is preempted
*/
if (owner)
retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
rcu_read_unlock();
/*
* If lock->owner is not set, the mutex has been released. Return true
* such that we'll trylock in the spin path, which is a faster option
* than the blocking slow path.
*/
return retval;
}
/*
* Optimistic spinning.
*
* We try to spin for acquisition when we find that the lock owner
* is currently running on a (different) CPU and while we don't
* need to reschedule. The rationale is that if the lock owner is
* running, it is likely to release the lock soon.
*
* The mutex spinners are queued up using MCS lock so that only one
* spinner can compete for the mutex. However, if mutex spinning isn't
* going to happen, there is no point in going through the lock/unlock
* overhead.
*
* Returns true when the lock was taken, otherwise false, indicating
* that we need to jump to the slowpath and sleep.
*
* The waiter flag is set to true if the spinner is a waiter in the wait
* queue. The waiter-spinner will spin on the lock directly and concurrently
* with the spinner at the head of the OSQ, if present, until the owner is
* changed to itself.
*/
static __always_inline bool
mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
const bool use_ww_ctx, struct mutex_waiter *waiter)
{
if (!waiter) {
/*
* The purpose of the mutex_can_spin_on_owner() function is
* to eliminate the overhead of osq_lock() and osq_unlock()
* in case spinning isn't possible. As a waiter-spinner
* is not going to take OSQ lock anyway, there is no need
* to call mutex_can_spin_on_owner().
*/
if (!mutex_can_spin_on_owner(lock))
goto fail;
/*
* In order to avoid a stampede of mutex spinners trying to
* acquire the mutex all at once, the spinners need to take a
* MCS (queued) lock first before spinning on the owner field.
*/
if (!osq_lock(&lock->osq))
goto fail;
}
for (;;) {
struct task_struct *owner;
/* Try to acquire the mutex... */
owner = __mutex_trylock_or_owner(lock);
if (!owner)
break;
/*
* There's an owner, wait for it to either
* release the lock or go to sleep.
*/
if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
goto fail_unlock;
/*
* The cpu_relax() call is a compiler barrier which forces
* everything in this loop to be re-loaded. We don't need
* memory barriers as we'll eventually observe the right
* values at the cost of a few extra spins.
*/
cpu_relax();
}
if (!waiter)
osq_unlock(&lock->osq);
return true;
fail_unlock:
if (!waiter)
osq_unlock(&lock->osq);
fail:
/*
* If we fell out of the spin path because of need_resched(),
* reschedule now, before we try-lock the mutex. This avoids getting
* scheduled out right after we obtained the mutex.
*/
if (need_resched()) {
/*
* We _should_ have TASK_RUNNING here, but just in case
* we do not, make it so, otherwise we might get stuck.
*/
__set_current_state(TASK_RUNNING);
schedule_preempt_disabled();
}
return false;
}
#else
static __always_inline bool
mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
const bool use_ww_ctx, struct mutex_waiter *waiter)
{
return false;
}
#endif
static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
/**
* mutex_unlock - release the mutex
* @lock: the mutex to be released
*
* Unlock a mutex that has been locked by this task previously.
*
* This function must not be used in interrupt context. Unlocking
* of a not locked mutex is not allowed.
*
* This function is similar to (but not equivalent to) up().
*/
void __sched mutex_unlock(struct mutex *lock)
{
#ifndef CONFIG_DEBUG_LOCK_ALLOC
if (__mutex_unlock_fast(lock))
return;
#endif
__mutex_unlock_slowpath(lock, _RET_IP_);
}
EXPORT_SYMBOL(mutex_unlock);
/**
* ww_mutex_unlock - release the w/w mutex
* @lock: the mutex to be released
*
* Unlock a mutex that has been locked by this task previously with any of the
* ww_mutex_lock* functions (with or without an acquire context). It is
* forbidden to release the locks after releasing the acquire context.
*
* This function must not be used in interrupt context. Unlocking
* of a unlocked mutex is not allowed.
*/
void __sched ww_mutex_unlock(struct ww_mutex *lock)
{
/*
* The unlocking fastpath is the 0->1 transition from 'locked'
* into 'unlocked' state:
*/
if (lock->ctx) {
#ifdef CONFIG_DEBUG_MUTEXES
DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
#endif
if (lock->ctx->acquired > 0)
lock->ctx->acquired--;
lock->ctx = NULL;
}
mutex_unlock(&lock->base);
}
EXPORT_SYMBOL(ww_mutex_unlock);
static __always_inline int __sched
__ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
{
if (ww_ctx->acquired > 0) {
#ifdef CONFIG_DEBUG_MUTEXES
struct ww_mutex *ww;
ww = container_of(lock, struct ww_mutex, base);
DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
ww_ctx->contending_lock = ww;
#endif
return -EDEADLK;
}
return 0;
}
/*
* Check the wound condition for the current lock acquire.
*
* Wound-Wait: If we're wounded, kill ourself.
*
* Wait-Die: If we're trying to acquire a lock already held by an older
* context, kill ourselves.
*
* Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
* look at waiters before us in the wait-list.
*/
static inline int __sched
__ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
struct ww_acquire_ctx *ctx)
{
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
struct mutex_waiter *cur;
if (ctx->acquired == 0)
return 0;
if (!ctx->is_wait_die) {
if (ctx->wounded)
return __ww_mutex_kill(lock, ctx);
return 0;
}
if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
return __ww_mutex_kill(lock, ctx);
/*
* If there is a waiter in front of us that has a context, then its
* stamp is earlier than ours and we must kill ourself.
*/
cur = waiter;
list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
if (!cur->ww_ctx)
continue;
return __ww_mutex_kill(lock, ctx);
}
return 0;
}
/*
* Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
* first. Such that older contexts are preferred to acquire the lock over
* younger contexts.
*
* Waiters without context are interspersed in FIFO order.
*
* Furthermore, for Wait-Die kill ourself immediately when possible (there are
* older contexts already waiting) to avoid unnecessary waiting and for
* Wound-Wait ensure we wound the owning context when it is younger.
*/
static inline int __sched
__ww_mutex_add_waiter(struct mutex_waiter *waiter,
struct mutex *lock,
struct ww_acquire_ctx *ww_ctx)
{
struct mutex_waiter *cur;
struct list_head *pos;
bool is_wait_die;
if (!ww_ctx) {
__mutex_add_waiter(lock, waiter, &lock->wait_list);
return 0;
}
is_wait_die = ww_ctx->is_wait_die;
/*
* Add the waiter before the first waiter with a higher stamp.
* Waiters without a context are skipped to avoid starving
* them. Wait-Die waiters may die here. Wound-Wait waiters
* never die here, but they are sorted in stamp order and
* may wound the lock holder.
*/
pos = &lock->wait_list;
list_for_each_entry_reverse(cur, &lock->wait_list, list) {
if (!cur->ww_ctx)
continue;
if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
/*
* Wait-Die: if we find an older context waiting, there
* is no point in queueing behind it, as we'd have to
* die the moment it would acquire the lock.
*/
if (is_wait_die) {
int ret = __ww_mutex_kill(lock, ww_ctx);
if (ret)
return ret;
}
break;
}
pos = &cur->list;
/* Wait-Die: ensure younger waiters die. */
__ww_mutex_die(lock, cur, ww_ctx);
}
__mutex_add_waiter(lock, waiter, pos);
/*
* Wound-Wait: if we're blocking on a mutex owned by a younger context,
* wound that such that we might proceed.
*/
if (!is_wait_die) {
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
/*
* See ww_mutex_set_context_fastpath(). Orders setting
* MUTEX_FLAG_WAITERS vs the ww->ctx load,
* such that either we or the fastpath will wound @ww->ctx.
*/
smp_mb();
__ww_mutex_wound(lock, ww_ctx, ww->ctx);
}
return 0;
}
/*
* Lock a mutex (possibly interruptible), slowpath:
*/
static __always_inline int __sched
__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
struct lockdep_map *nest_lock, unsigned long ip,
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
{
struct mutex_waiter waiter;
bool first = false;
struct ww_mutex *ww;
int ret;
might_sleep();
ww = container_of(lock, struct ww_mutex, base);
if (use_ww_ctx && ww_ctx) {
if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
return -EALREADY;
/*
* Reset the wounded flag after a kill. No other process can
* race and wound us here since they can't have a valid owner
* pointer if we don't have any locks held.
*/
if (ww_ctx->acquired == 0)
ww_ctx->wounded = 0;
}
preempt_disable();
mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
if (__mutex_trylock(lock) ||
mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
/* got the lock, yay! */
lock_acquired(&lock->dep_map, ip);
if (use_ww_ctx && ww_ctx)
ww_mutex_set_context_fastpath(ww, ww_ctx);
preempt_enable();
return 0;
}
spin_lock(&lock->wait_lock);
/*
* After waiting to acquire the wait_lock, try again.
*/
if (__mutex_trylock(lock)) {
if (use_ww_ctx && ww_ctx)
__ww_mutex_check_waiters(lock, ww_ctx);
goto skip_wait;
}
debug_mutex_lock_common(lock, &waiter);
lock_contended(&lock->dep_map, ip);
if (!use_ww_ctx) {
/* add waiting tasks to the end of the waitqueue (FIFO): */
__mutex_add_waiter(lock, &waiter, &lock->wait_list);
#ifdef CONFIG_DEBUG_MUTEXES
waiter.ww_ctx = MUTEX_POISON_WW_CTX;
#endif
} else {
/*
* Add in stamp order, waking up waiters that must kill
* themselves.
*/
ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
if (ret)
goto err_early_kill;
waiter.ww_ctx = ww_ctx;
}
waiter.task = current;
set_current_state(state);
for (;;) {
/*
* Once we hold wait_lock, we're serialized against
* mutex_unlock() handing the lock off to us, do a trylock
* before testing the error conditions to make sure we pick up
* the handoff.
*/
if (__mutex_trylock(lock))
goto acquired;
/*
* Check for signals and kill conditions while holding
* wait_lock. This ensures the lock cancellation is ordered
* against mutex_unlock() and wake-ups do not go missing.
*/
if (signal_pending_state(state, current)) {
ret = -EINTR;
goto err;
}
if (use_ww_ctx && ww_ctx) {
ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
if (ret)
goto err;
}
spin_unlock(&lock->wait_lock);
schedule_preempt_disabled();
/*
* ww_mutex needs to always recheck its position since its waiter
* list is not FIFO ordered.
*/
if ((use_ww_ctx && ww_ctx) || !first) {
first = __mutex_waiter_is_first(lock, &waiter);
if (first)
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
}
set_current_state(state);
/*
* Here we order against unlock; we must either see it change
* state back to RUNNING and fall through the next schedule(),
* or we must see its unlock and acquire.
*/
if (__mutex_trylock(lock) ||
(first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
break;
spin_lock(&lock->wait_lock);
}
spin_lock(&lock->wait_lock);
acquired:
__set_current_state(TASK_RUNNING);
if (use_ww_ctx && ww_ctx) {
/*
* Wound-Wait; we stole the lock (!first_waiter), check the
* waiters as anyone might want to wound us.
*/
if (!ww_ctx->is_wait_die &&
!__mutex_waiter_is_first(lock, &waiter))
__ww_mutex_check_waiters(lock, ww_ctx);
}
mutex_remove_waiter(lock, &waiter, current);
if (likely(list_empty(&lock->wait_list)))
__mutex_clear_flag(lock, MUTEX_FLAGS);
debug_mutex_free_waiter(&waiter);
skip_wait:
/* got the lock - cleanup and rejoice! */
lock_acquired(&lock->dep_map, ip);
if (use_ww_ctx && ww_ctx)
ww_mutex_lock_acquired(ww, ww_ctx);
spin_unlock(&lock->wait_lock);
preempt_enable();
return 0;
err:
__set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, current);
err_early_kill:
spin_unlock(&lock->wait_lock);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, 1, ip);
preempt_enable();
return ret;
}
static int __sched
__mutex_lock(struct mutex *lock, long state, unsigned int subclass,
struct lockdep_map *nest_lock, unsigned long ip)
{
return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
}
static int __sched
__ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
struct lockdep_map *nest_lock, unsigned long ip,
struct ww_acquire_ctx *ww_ctx)
{
return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
void __sched
mutex_lock_nested(struct mutex *lock, unsigned int subclass)
{
__mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
}
EXPORT_SYMBOL_GPL(mutex_lock_nested);
void __sched
_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
{
__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
}
EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
int __sched
mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
{
return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
}
EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
int __sched
mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
{
return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
}
EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
void __sched
mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
{
int token;
might_sleep();
token = io_schedule_prepare();
__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
subclass, NULL, _RET_IP_, NULL, 0);
io_schedule_finish(token);
}
EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
static inline int
ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
unsigned tmp;
if (ctx->deadlock_inject_countdown-- == 0) {
tmp = ctx->deadlock_inject_interval;
if (tmp > UINT_MAX/4)
tmp = UINT_MAX;
else
tmp = tmp*2 + tmp + tmp/2;
ctx->deadlock_inject_interval = tmp;
ctx->deadlock_inject_countdown = tmp;
ctx->contending_lock = lock;
ww_mutex_unlock(lock);
return -EDEADLK;
}
#endif
return 0;
}
int __sched
ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
int ret;
might_sleep();
ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
ctx);
if (!ret && ctx && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
return ret;
}
EXPORT_SYMBOL_GPL(ww_mutex_lock);
int __sched
ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
int ret;
might_sleep();
ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
ctx);
if (!ret && ctx && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
return ret;
}
EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
#endif
/*
* Release the lock, slowpath:
*/
static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
{
struct task_struct *next = NULL;
DEFINE_WAKE_Q(wake_q);
unsigned long owner;
mutex_release(&lock->dep_map, 1, ip);
/*
* Release the lock before (potentially) taking the spinlock such that
* other contenders can get on with things ASAP.
*
* Except when HANDOFF, in that case we must not clear the owner field,
* but instead set it to the top waiter.
*/
owner = atomic_long_read(&lock->owner);
for (;;) {
unsigned long old;
#ifdef CONFIG_DEBUG_MUTEXES
DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
#endif
if (owner & MUTEX_FLAG_HANDOFF)
break;
old = atomic_long_cmpxchg_release(&lock->owner, owner,
__owner_flags(owner));
if (old == owner) {
if (owner & MUTEX_FLAG_WAITERS)
break;
return;
}
owner = old;
}
spin_lock(&lock->wait_lock);
debug_mutex_unlock(lock);
if (!list_empty(&lock->wait_list)) {
/* get the first entry from the wait-list: */
struct mutex_waiter *waiter =
list_first_entry(&lock->wait_list,
struct mutex_waiter, list);
next = waiter->task;
debug_mutex_wake_waiter(lock, waiter);
wake_q_add(&wake_q, next);
}
if (owner & MUTEX_FLAG_HANDOFF)
__mutex_handoff(lock, next);
spin_unlock(&lock->wait_lock);
wake_up_q(&wake_q);
}
#ifndef CONFIG_DEBUG_LOCK_ALLOC
/*
* Here come the less common (and hence less performance-critical) APIs:
* mutex_lock_interruptible() and mutex_trylock().
*/
static noinline int __sched
__mutex_lock_killable_slowpath(struct mutex *lock);
static noinline int __sched
__mutex_lock_interruptible_slowpath(struct mutex *lock);
/**
* mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
* @lock: The mutex to be acquired.
*
* Lock the mutex like mutex_lock(). If a signal is delivered while the
* process is sleeping, this function will return without acquiring the
* mutex.
*
* Context: Process context.
* Return: 0 if the lock was successfully acquired or %-EINTR if a
* signal arrived.
*/
int __sched mutex_lock_interruptible(struct mutex *lock)
{
might_sleep();
if (__mutex_trylock_fast(lock))
return 0;
return __mutex_lock_interruptible_slowpath(lock);
}
EXPORT_SYMBOL(mutex_lock_interruptible);
/**
* mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
* @lock: The mutex to be acquired.
*
* Lock the mutex like mutex_lock(). If a signal which will be fatal to
* the current process is delivered while the process is sleeping, this
* function will return without acquiring the mutex.
*
* Context: Process context.
* Return: 0 if the lock was successfully acquired or %-EINTR if a
* fatal signal arrived.
*/
int __sched mutex_lock_killable(struct mutex *lock)
{
might_sleep();
if (__mutex_trylock_fast(lock))
return 0;
return __mutex_lock_killable_slowpath(lock);
}
EXPORT_SYMBOL(mutex_lock_killable);
/**
* mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
* @lock: The mutex to be acquired.
*
* Lock the mutex like mutex_lock(). While the task is waiting for this
* mutex, it will be accounted as being in the IO wait state by the
* scheduler.
*
* Context: Process context.
*/
void __sched mutex_lock_io(struct mutex *lock)
{
int token;
token = io_schedule_prepare();
mutex_lock(lock);
io_schedule_finish(token);
}
EXPORT_SYMBOL_GPL(mutex_lock_io);
static noinline void __sched
__mutex_lock_slowpath(struct mutex *lock)
{
__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
}
static noinline int __sched
__mutex_lock_killable_slowpath(struct mutex *lock)
{
return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
}
static noinline int __sched
__mutex_lock_interruptible_slowpath(struct mutex *lock)
{
return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
}
static noinline int __sched
__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
_RET_IP_, ctx);
}
static noinline int __sched
__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
_RET_IP_, ctx);
}
#endif
/**
* mutex_trylock - try to acquire the mutex, without waiting
* @lock: the mutex to be acquired
*
* Try to acquire the mutex atomically. Returns 1 if the mutex
* has been acquired successfully, and 0 on contention.
*
* NOTE: this function follows the spin_trylock() convention, so
* it is negated from the down_trylock() return values! Be careful
* about this when converting semaphore users to mutexes.
*
* This function must not be used in interrupt context. The
* mutex must be released by the same task that acquired it.
*/
int __sched mutex_trylock(struct mutex *lock)
{
bool locked = __mutex_trylock(lock);
if (locked)
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
return locked;
}
EXPORT_SYMBOL(mutex_trylock);
#ifndef CONFIG_DEBUG_LOCK_ALLOC
int __sched
ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
might_sleep();
if (__mutex_trylock_fast(&lock->base)) {
if (ctx)
ww_mutex_set_context_fastpath(lock, ctx);
return 0;
}
return __ww_mutex_lock_slowpath(lock, ctx);
}
EXPORT_SYMBOL(ww_mutex_lock);
int __sched
ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
might_sleep();
if (__mutex_trylock_fast(&lock->base)) {
if (ctx)
ww_mutex_set_context_fastpath(lock, ctx);
return 0;
}
return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
}
EXPORT_SYMBOL(ww_mutex_lock_interruptible);
#endif
/**
* atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
* @cnt: the atomic which we are to dec
* @lock: the mutex to return holding if we dec to 0
*
* return true and hold lock if we dec to 0, return false otherwise
*/
int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
{
/* dec if we can't possibly hit 0 */
if (atomic_add_unless(cnt, -1, 1))
return 0;
/* we might hit 0, so take the lock */
mutex_lock(lock);
if (!atomic_dec_and_test(cnt)) {
/* when we actually did the dec, we didn't hit 0 */
mutex_unlock(lock);
return 0;
}
/* we hit 0, and we hold the lock */
return 1;
}
EXPORT_SYMBOL(atomic_dec_and_mutex_lock);