| Message ID | 20191019170141.GQ18794@devbig004.ftw2.facebook.com |
|---|---|
| State | Changes Requested |
| Delegated to: | David Miller |
| Headers | show |
| Series | net: fix sk_page_frag() recursion from memory reclaim | expand |
On 10/19/19 10:01 AM, Tejun Heo wrote: > From f0335a5d14d3596d36e3ffddb2fd4fa0dc6ca9c2 Mon Sep 17 00:00:00 2001 > From: Tejun Heo <tj@kernel.org> > Date: Sat, 19 Oct 2019 09:10:57 -0700 > > 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 updating sk_page_frag() to test __GFP_MEMALLOC and not use > current->task_frag if set. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Cc: Josef Bacik <josef@toxicpanda.com> > Cc: stable@vger.kernel.org > --- > include/net/sock.h | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/include/net/sock.h b/include/net/sock.h > index 2c53f1a1d905..4e2ca38acc3c 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -2233,12 +2233,21 @@ 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 there can be no other users. > + * > + * 1. The socket allocation mode allows current thread to sleep. This is > + * the sleepable context which owns the task page_frag. > + * > + * 2. The socket allocation mode doesn't indicate that the socket is being > + * used to reclaim memory. Memory 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_allow_blocking(sk->sk_allocation) && > + !(sk->sk_allocation & __GFP_MEMALLOC)) > return ¤t->task_frag; > > return &sk->sk_frag; > It seems compiler generates better code with : diff --git a/include/net/sock.h b/include/net/sock.h index ab905c4b1f0efd42ebdcae333b3f0a2c7c1b2248..56de6ac99f0952bd0bc003353c094ce3a5a852f4 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -2238,7 +2238,8 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp, */ static inline struct page_frag *sk_page_frag(struct sock *sk) { - if (gfpflags_allow_blocking(sk->sk_allocation)) + if (likely((sk->sk_allocation & (__GFP_DIRECT_RECLAIM | __GFP_MEMALLOC)) == + __GFP_DIRECT_RECLAIM)) return ¤t->task_frag; return &sk->sk_frag; WDYT ? Thanks !
Hello, On Sat, Oct 19, 2019 at 11:15:28AM -0700, Eric Dumazet wrote: > It seems compiler generates better code with : > > diff --git a/include/net/sock.h b/include/net/sock.h > index ab905c4b1f0efd42ebdcae333b3f0a2c7c1b2248..56de6ac99f0952bd0bc003353c094ce3a5a852f4 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -2238,7 +2238,8 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp, > */ > static inline struct page_frag *sk_page_frag(struct sock *sk) > { > - if (gfpflags_allow_blocking(sk->sk_allocation)) > + if (likely((sk->sk_allocation & (__GFP_DIRECT_RECLAIM | __GFP_MEMALLOC)) == > + __GFP_DIRECT_RECLAIM)) > return ¤t->task_frag; > > return &sk->sk_frag; > > > WDYT ? Whatever works is fine by me. gfpflags_allow_blocking() is clearer than testing __GFP_DIRECT_RECLAIM directly tho. Maybe a better way is introducing a new gfpflags_ helper? Thanks.
On 10/19/19 2:18 PM, Tejun Heo wrote: > Whatever works is fine by me. gfpflags_allow_blocking() is clearer > than testing __GFP_DIRECT_RECLAIM directly tho. Maybe a better way is > introducing a new gfpflags_ helper? Sounds good to me !
On Sat, 19 Oct 2019 14:25:57 -0700, Eric Dumazet wrote: > On 10/19/19 2:18 PM, Tejun Heo wrote: > > > Whatever works is fine by me. gfpflags_allow_blocking() is clearer > > than testing __GFP_DIRECT_RECLAIM directly tho. Maybe a better way is > > introducing a new gfpflags_ helper? > > Sounds good to me ! IIUC there will be a v2 with a new helper, dropping this from patchwork.
diff --git a/include/net/sock.h b/include/net/sock.h index 2c53f1a1d905..4e2ca38acc3c 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -2233,12 +2233,21 @@ 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 there can be no other users. + * + * 1. The socket allocation mode allows current thread to sleep. This is + * the sleepable context which owns the task page_frag. + * + * 2. The socket allocation mode doesn't indicate that the socket is being + * used to reclaim memory. Memory 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_allow_blocking(sk->sk_allocation) && + !(sk->sk_allocation & __GFP_MEMALLOC)) return ¤t->task_frag; return &sk->sk_frag;