| From 1a3cfa10a0d7845c158157cba4dbda245ed20517 Mon Sep 17 00:00:00 2001 |
| From: Tejun Heo <tj@kernel.org> |
| Date: Thu, 24 Oct 2019 13:50:27 -0700 |
| Subject: [PATCH] net: fix sk_page_frag() recursion from memory reclaim |
| |
| commit 20eb4f29b60286e0d6dc01d9c260b4bd383c58fb upstream. |
| |
| sk_page_frag() optimizes skb_frag allocations by using per-task |
| skb_frag cache when it knows it's the only user. The condition is |
| determined by seeing whether the socket allocation mask allows |
| blocking - if the allocation may block, it obviously owns the task's |
| context and ergo exclusively owns current->task_frag. |
| |
| Unfortunately, this misses recursion through memory reclaim path. |
| Please take a look at the following backtrace. |
| |
| [2] RIP: 0010:tcp_sendmsg_locked+0xccf/0xe10 |
| ... |
| tcp_sendmsg+0x27/0x40 |
| sock_sendmsg+0x30/0x40 |
| sock_xmit.isra.24+0xa1/0x170 [nbd] |
| nbd_send_cmd+0x1d2/0x690 [nbd] |
| nbd_queue_rq+0x1b5/0x3b0 [nbd] |
| __blk_mq_try_issue_directly+0x108/0x1b0 |
| blk_mq_request_issue_directly+0xbd/0xe0 |
| blk_mq_try_issue_list_directly+0x41/0xb0 |
| blk_mq_sched_insert_requests+0xa2/0xe0 |
| blk_mq_flush_plug_list+0x205/0x2a0 |
| blk_flush_plug_list+0xc3/0xf0 |
| [1] blk_finish_plug+0x21/0x2e |
| _xfs_buf_ioapply+0x313/0x460 |
| __xfs_buf_submit+0x67/0x220 |
| xfs_buf_read_map+0x113/0x1a0 |
| xfs_trans_read_buf_map+0xbf/0x330 |
| xfs_btree_read_buf_block.constprop.42+0x95/0xd0 |
| xfs_btree_lookup_get_block+0x95/0x170 |
| xfs_btree_lookup+0xcc/0x470 |
| xfs_bmap_del_extent_real+0x254/0x9a0 |
| __xfs_bunmapi+0x45c/0xab0 |
| xfs_bunmapi+0x15/0x30 |
| xfs_itruncate_extents_flags+0xca/0x250 |
| xfs_free_eofblocks+0x181/0x1e0 |
| xfs_fs_destroy_inode+0xa8/0x1b0 |
| destroy_inode+0x38/0x70 |
| dispose_list+0x35/0x50 |
| prune_icache_sb+0x52/0x70 |
| super_cache_scan+0x120/0x1a0 |
| do_shrink_slab+0x120/0x290 |
| shrink_slab+0x216/0x2b0 |
| shrink_node+0x1b6/0x4a0 |
| do_try_to_free_pages+0xc6/0x370 |
| try_to_free_mem_cgroup_pages+0xe3/0x1e0 |
| try_charge+0x29e/0x790 |
| mem_cgroup_charge_skmem+0x6a/0x100 |
| __sk_mem_raise_allocated+0x18e/0x390 |
| __sk_mem_schedule+0x2a/0x40 |
| [0] tcp_sendmsg_locked+0x8eb/0xe10 |
| tcp_sendmsg+0x27/0x40 |
| sock_sendmsg+0x30/0x40 |
| ___sys_sendmsg+0x26d/0x2b0 |
| __sys_sendmsg+0x57/0xa0 |
| do_syscall_64+0x42/0x100 |
| entry_SYSCALL_64_after_hwframe+0x44/0xa9 |
| |
| In [0], tcp_send_msg_locked() was using current->page_frag when it |
| called sk_wmem_schedule(). It already calculated how many bytes can |
| be fit into current->page_frag. Due to memory pressure, |
| sk_wmem_schedule() called into memory reclaim path which called into |
| xfs and then IO issue path. Because the filesystem in question is |
| backed by nbd, the control goes back into the tcp layer - back into |
| tcp_sendmsg_locked(). |
| |
| nbd sets sk_allocation to (GFP_NOIO | __GFP_MEMALLOC) which makes |
| sense - it's in the process of freeing memory and wants to be able to, |
| e.g., drop clean pages to make forward progress. However, this |
| confused sk_page_frag() called from [2]. Because it only tests |
| whether the allocation allows blocking which it does, it now thinks |
| current->page_frag can be used again although it already was being |
| used in [0]. |
| |
| After [2] used current->page_frag, the offset would be increased by |
| the used amount. When the control returns to [0], |
| current->page_frag's offset is increased and the previously calculated |
| number of bytes now may overrun the end of allocated memory leading to |
| silent memory corruptions. |
| |
| Fix it by adding gfpflags_normal_context() which tests sleepable && |
| !reclaim and use it to determine whether to use current->task_frag. |
| |
| v2: Eric didn't like gfp flags being tested twice. Introduce a new |
| helper gfpflags_normal_context() and combine the two tests. |
| |
| Signed-off-by: Tejun Heo <tj@kernel.org> |
| Cc: Josef Bacik <josef@toxicpanda.com> |
| Cc: Eric Dumazet <eric.dumazet@gmail.com> |
| Cc: stable@vger.kernel.org |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/include/linux/gfp.h b/include/linux/gfp.h |
| index fb07b503dc45..61f2f6ff9467 100644 |
| --- a/include/linux/gfp.h |
| +++ b/include/linux/gfp.h |
| @@ -325,6 +325,29 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags) |
| return !!(gfp_flags & __GFP_DIRECT_RECLAIM); |
| } |
| |
| +/** |
| + * gfpflags_normal_context - is gfp_flags a normal sleepable context? |
| + * @gfp_flags: gfp_flags to test |
| + * |
| + * Test whether @gfp_flags indicates that the allocation is from the |
| + * %current context and allowed to sleep. |
| + * |
| + * An allocation being allowed to block doesn't mean it owns the %current |
| + * context. When direct reclaim path tries to allocate memory, the |
| + * allocation context is nested inside whatever %current was doing at the |
| + * time of the original allocation. The nested allocation may be allowed |
| + * to block but modifying anything %current owns can corrupt the outer |
| + * context's expectations. |
| + * |
| + * %true result from this function indicates that the allocation context |
| + * can sleep and use anything that's associated with %current. |
| + */ |
| +static inline bool gfpflags_normal_context(const gfp_t gfp_flags) |
| +{ |
| + return (gfp_flags & (__GFP_DIRECT_RECLAIM | __GFP_MEMALLOC)) == |
| + __GFP_DIRECT_RECLAIM; |
| +} |
| + |
| #ifdef CONFIG_HIGHMEM |
| #define OPT_ZONE_HIGHMEM ZONE_HIGHMEM |
| #else |
| diff --git a/include/net/sock.h b/include/net/sock.h |
| index 8e6e348017f3..f637c1da8f05 100644 |
| --- a/include/net/sock.h |
| +++ b/include/net/sock.h |
| @@ -2233,12 +2233,17 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp, |
| * sk_page_frag - return an appropriate page_frag |
| * @sk: socket |
| * |
| - * If socket allocation mode allows current thread to sleep, it means its |
| - * safe to use the per task page_frag instead of the per socket one. |
| + * Use the per task page_frag instead of the per socket one for |
| + * optimization when we know that we're in the normal context and owns |
| + * everything that's associated with %current. |
| + * |
| + * gfpflags_allow_blocking() isn't enough here as direct reclaim may nest |
| + * inside other socket operations and end up recursing into sk_page_frag() |
| + * while it's already in use. |
| */ |
| static inline struct page_frag *sk_page_frag(struct sock *sk) |
| { |
| - if (gfpflags_allow_blocking(sk->sk_allocation)) |
| + if (gfpflags_normal_context(sk->sk_allocation)) |
| return ¤t->task_frag; |
| |
| return &sk->sk_frag; |
| -- |
| 2.7.4 |
| |