| Message ID | 20211124094317.69719-1-ligang.bdlg@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] shmem: fix a race between shmem_unused_huge_shrink and shmem_evict_inode | expand |
On Wed, Nov 24, 2021 at 05:43:16PM +0800, Gang Li wrote: > +move_back: > + /* inodes that are on @list and will not be deleted must be moved back to > + * global list before iput for two reasons: > + * 1. iput in lock: iput call shmem_evict_inode, then cause deadlock. > + * 2. iput before lock: shmem_evict_inode may grab the inode on @list, > + * which will cause race. > + */ > + spin_lock(&sbinfo->shrinklist_lock); > + list_move(&info->shrinklist, &sbinfo->shrinklist); > + sbinfo->shrinklist_len++; > + spin_unlock(&sbinfo->shrinklist_lock); > +put: > iput(inode); > } > > - spin_lock(&sbinfo->shrinklist_lock); > - list_splice_tail(&list, &sbinfo->shrinklist); > - sbinfo->shrinklist_len -= removed; > - spin_unlock(&sbinfo->shrinklist_lock); > - > return split; > } Okay, I guess it works. Locking is not pretty, but well.. Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
On Wed, Nov 24, 2021 at 5:43 PM Gang Li <ligang.bdlg@bytedance.com> wrote: > > This patch fixes a data race in commit 779750d20b93 ("shmem: split huge pages > beyond i_size under memory pressure"). > > Here are call traces: > > Call Trace 1: > shmem_unused_huge_shrink+0x3ae/0x410 > ? __list_lru_walk_one.isra.5+0x33/0x160 > super_cache_scan+0x17c/0x190 > shrink_slab.part.55+0x1ef/0x3f0 > shrink_node+0x10e/0x330 > kswapd+0x380/0x740 > kthread+0xfc/0x130 > ? mem_cgroup_shrink_node+0x170/0x170 > ? kthread_create_on_node+0x70/0x70 > ret_from_fork+0x1f/0x30 > > Call Trace 2: > shmem_evict_inode+0xd8/0x190 > evict+0xbe/0x1c0 > do_unlinkat+0x137/0x330 > do_syscall_64+0x76/0x120 > entry_SYSCALL_64_after_hwframe+0x3d/0xa2 > > The simultaneous deletion of adjacent elements in the local list (@list) > by shmem_unused_huge_shrink and shmem_evict_inode will break the list. > > Image there are 3 items in the local list (@list). > In the first traversal, A is not deleted from @list. > > 1) A->B->C > ^ > | > pos (leave) > > In the second traversal, B is deleted from @list. Concurrently, A is > deleted from @list through shmem_evict_inode() since last reference counter of > inode is dropped by other thread. Then the @list is corrupted. > > 2) A->B->C > ^ ^ > | | > evict pos (drop) > > Fix: > > We should make sure the item is either on the global list or deleted from > any local list before iput(). > > Fixed by moving inodes that are on @list and will not be deleted back to > global list before iput. > > Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure") > Signed-off-by: Gang Li <ligang.bdlg@bytedance.com> > > --- > > Changes in v3: > - Add more comment. > - Use list_move(&info->shrinklist, &sbinfo->shrinklist) instead of > list_move(pos, &sbinfo->shrinklist) for consistency. > > Changes in v2: https://lore.kernel.org/all/20211124030840.88455-1-ligang.bdlg@bytedance.com/ > - Move spinlock to the front of iput instead of changing lock type > since iput will call evict which may cause deadlock by requesting > shrinklist_lock. > - Add call trace in commit message. > > v1: https://lore.kernel.org/lkml/20211122064126.76734-1-ligang.bdlg@bytedance.com/ > > --- > mm/shmem.c | 35 ++++++++++++++++++++--------------- > 1 file changed, 20 insertions(+), 15 deletions(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 9023103ee7d8..ab2df692bd58 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -569,7 +569,6 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, > /* inode is about to be evicted */ > if (!inode) { > list_del_init(&info->shrinklist); > - removed++; > goto next; > } > > @@ -577,15 +576,16 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, > if (round_up(inode->i_size, PAGE_SIZE) == > round_up(inode->i_size, HPAGE_PMD_SIZE)) { > list_move(&info->shrinklist, &to_remove); > - removed++; > goto next; > } > > list_move(&info->shrinklist, &list); > next: > + removed++; > if (!--batch) > break; > } > + sbinfo->shrinklist_len -= removed; > spin_unlock(&sbinfo->shrinklist_lock); > > list_for_each_safe(pos, next, &to_remove) { > @@ -602,7 +602,7 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, > inode = &info->vfs_inode; > > if (nr_to_split && split >= nr_to_split) > - goto leave; > + goto move_back; > > page = find_get_page(inode->i_mapping, > (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT); > @@ -616,38 +616,43 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, > } > > /* > - * Leave the inode on the list if we failed to lock > - * the page at this time. > + * Move the inode on the list back to shrinklist if we failed > + * to lock the page at this time. > * > * Waiting for the lock may lead to deadlock in the > * reclaim path. > */ > if (!trylock_page(page)) { > put_page(page); > - goto leave; > + goto move_back; > } > > ret = split_huge_page(page); > unlock_page(page); > put_page(page); > > - /* If split failed leave the inode on the list */ > + /* If split failed move the inode on the list back to shrinklist */ > if (ret) > - goto leave; > + goto move_back; > > split++; > drop: > list_del_init(&info->shrinklist); > - removed++; > -leave: > + goto put; > +move_back: > + /* inodes that are on @list and will not be deleted must be moved back to > + * global list before iput for two reasons: > + * 1. iput in lock: iput call shmem_evict_inode, then cause deadlock. > + * 2. iput before lock: shmem_evict_inode may grab the inode on @list, > + * which will cause race. > + */ Multi-line comment is like the following format. /* * Comment here. */ And I also suggest reworking the comments here. Something like: /* * Make sure the inode is either on the global list or deleted from * any local list before iput() since it could be deleted in another * thread once we put the inode (then the local list is corrupted). */ With that. Reviewed-by: Muchun Song <songmuchun@bytedance.com> > + spin_lock(&sbinfo->shrinklist_lock); > + list_move(&info->shrinklist, &sbinfo->shrinklist); > + sbinfo->shrinklist_len++; > + spin_unlock(&sbinfo->shrinklist_lock); > +put: > iput(inode); > } > > - spin_lock(&sbinfo->shrinklist_lock); > - list_splice_tail(&list, &sbinfo->shrinklist); > - sbinfo->shrinklist_len -= removed; > - spin_unlock(&sbinfo->shrinklist_lock); > - > return split; > } > > -- > 2.20.1 >
diff --git a/mm/shmem.c b/mm/shmem.c index 9023103ee7d8..ab2df692bd58 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -569,7 +569,6 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, /* inode is about to be evicted */ if (!inode) { list_del_init(&info->shrinklist); - removed++; goto next; } @@ -577,15 +576,16 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, if (round_up(inode->i_size, PAGE_SIZE) == round_up(inode->i_size, HPAGE_PMD_SIZE)) { list_move(&info->shrinklist, &to_remove); - removed++; goto next; } list_move(&info->shrinklist, &list); next: + removed++; if (!--batch) break; } + sbinfo->shrinklist_len -= removed; spin_unlock(&sbinfo->shrinklist_lock); list_for_each_safe(pos, next, &to_remove) { @@ -602,7 +602,7 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, inode = &info->vfs_inode; if (nr_to_split && split >= nr_to_split) - goto leave; + goto move_back; page = find_get_page(inode->i_mapping, (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT); @@ -616,38 +616,43 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, } /* - * Leave the inode on the list if we failed to lock - * the page at this time. + * Move the inode on the list back to shrinklist if we failed + * to lock the page at this time. * * Waiting for the lock may lead to deadlock in the * reclaim path. */ if (!trylock_page(page)) { put_page(page); - goto leave; + goto move_back; } ret = split_huge_page(page); unlock_page(page); put_page(page); - /* If split failed leave the inode on the list */ + /* If split failed move the inode on the list back to shrinklist */ if (ret) - goto leave; + goto move_back; split++; drop: list_del_init(&info->shrinklist); - removed++; -leave: + goto put; +move_back: + /* inodes that are on @list and will not be deleted must be moved back to + * global list before iput for two reasons: + * 1. iput in lock: iput call shmem_evict_inode, then cause deadlock. + * 2. iput before lock: shmem_evict_inode may grab the inode on @list, + * which will cause race. + */ + spin_lock(&sbinfo->shrinklist_lock); + list_move(&info->shrinklist, &sbinfo->shrinklist); + sbinfo->shrinklist_len++; + spin_unlock(&sbinfo->shrinklist_lock); +put: iput(inode); } - spin_lock(&sbinfo->shrinklist_lock); - list_splice_tail(&list, &sbinfo->shrinklist); - sbinfo->shrinklist_len -= removed; - spin_unlock(&sbinfo->shrinklist_lock); - return split; }
This patch fixes a data race in commit 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure"). Here are call traces: Call Trace 1: shmem_unused_huge_shrink+0x3ae/0x410 ? __list_lru_walk_one.isra.5+0x33/0x160 super_cache_scan+0x17c/0x190 shrink_slab.part.55+0x1ef/0x3f0 shrink_node+0x10e/0x330 kswapd+0x380/0x740 kthread+0xfc/0x130 ? mem_cgroup_shrink_node+0x170/0x170 ? kthread_create_on_node+0x70/0x70 ret_from_fork+0x1f/0x30 Call Trace 2: shmem_evict_inode+0xd8/0x190 evict+0xbe/0x1c0 do_unlinkat+0x137/0x330 do_syscall_64+0x76/0x120 entry_SYSCALL_64_after_hwframe+0x3d/0xa2 The simultaneous deletion of adjacent elements in the local list (@list) by shmem_unused_huge_shrink and shmem_evict_inode will break the list. Image there are 3 items in the local list (@list). In the first traversal, A is not deleted from @list. 1) A->B->C ^ | pos (leave) In the second traversal, B is deleted from @list. Concurrently, A is deleted from @list through shmem_evict_inode() since last reference counter of inode is dropped by other thread. Then the @list is corrupted. 2) A->B->C ^ ^ | | evict pos (drop) Fix: We should make sure the item is either on the global list or deleted from any local list before iput(). Fixed by moving inodes that are on @list and will not be deleted back to global list before iput. Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure") Signed-off-by: Gang Li <ligang.bdlg@bytedance.com> --- Changes in v3: - Add more comment. - Use list_move(&info->shrinklist, &sbinfo->shrinklist) instead of list_move(pos, &sbinfo->shrinklist) for consistency. Changes in v2: https://lore.kernel.org/all/20211124030840.88455-1-ligang.bdlg@bytedance.com/ - Move spinlock to the front of iput instead of changing lock type since iput will call evict which may cause deadlock by requesting shrinklist_lock. - Add call trace in commit message. v1: https://lore.kernel.org/lkml/20211122064126.76734-1-ligang.bdlg@bytedance.com/ --- mm/shmem.c | 35 ++++++++++++++++++++--------------- 1 file changed, 20 insertions(+), 15 deletions(-)