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Miller" , netdev@vger.kernel.org, Kernel Team , LKML , Josef Bacik , Eric Dumazet , Jakub Kicinski , Johannes Weiner , Linux MM , Mel Gorman , Andrew Morton Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: +Michal Hocko On Thu, Oct 24, 2019 at 1:50 PM Tejun Heo wrote: > > 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 > Cc: Josef Bacik > Cc: Eric Dumazet > Cc: stable@vger.kernel.org > --- > include/linux/gfp.h | 23 +++++++++++++++++++++++ > include/net/sock.h | 11 ++++++++--- > 2 files changed, 31 insertions(+), 3 deletions(-) > > 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; I think we should be checking PF_MEMALLOC here instead. Something like: return gfpflags_allow_blocking(gfp_flags) && !(current->flags & PF_MEMALLOC); In my limited understanding, __GFP_MEMALLOC gives access to reserve but we have overloaded PF_MEMALLOC to also define the reclaim context. There are PF_MEMALLOC users which does not use __GFP_MEMALLOC like iscsi_sw_tcp_pdu_xmit() which can call sock_sendmsg(). > +} > + > #ifdef CONFIG_HIGHMEM > #define OPT_ZONE_HIGHMEM ZONE_HIGHMEM > #else > diff --git a/include/net/sock.h b/include/net/sock.h > index f69b58bff7e5..c31a9ed86d5a 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -2242,12 +2242,17 @@ 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;