Re: [PATCH V3] inotify: Fix possible deadlock in fsnotify_destroy_mark

Amir Goldstein
2024-09-27T14:58:47Z

On Fri, Sep 27, 2024 at 4:36 PM Lizhi Xu <lizhi.xu@windriver.com> wrote:
>
> [Syzbot reported]
> WARNING: possible circular locking dependency detected
> 6.11.0-rc4-syzkaller-00019-gb311c1b497e5 #0 Not tainted
> ------------------------------------------------------
> kswapd0/78 is trying to acquire lock:
> ffff88801b8d8930 (&group->mark_mutex){+.+.}-{3:3}, at: fsnotify_group_lock include/linux/fsnotify_backend.h:270 [inline]
> ffff88801b8d8930 (&group->mark_mutex){+.+.}-{3:3}, at: fsnotify_destroy_mark+0x38/0x3c0 fs/notify/mark.c:578
>
> but task is already holding lock:
> ffffffff8ea2fd60 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:6841 [inline]
> ffffffff8ea2fd60 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0xbb4/0x35a0 mm/vmscan.c:7223
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (fs_reclaim){+.+.}-{0:0}:
> lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
> __fs_reclaim_acquire mm/page_alloc.c:3818 [inline]
> fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3832
> might_alloc include/linux/sched/mm.h:334 [inline]
> slab_pre_alloc_hook mm/slub.c:3939 [inline]
> slab_alloc_node mm/slub.c:4017 [inline]
> kmem_cache_alloc_noprof+0x3d/0x2a0 mm/slub.c:4044
> inotify_new_watch fs/notify/inotify/inotify_user.c:599 [inline]
> inotify_update_watch fs/notify/inotify/inotify_user.c:647 [inline]
> __do_sys_inotify_add_watch fs/notify/inotify/inotify_user.c:786 [inline]
> __se_sys_inotify_add_watch+0x72e/0x1070 fs/notify/inotify/inotify_user.c:729
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> -> #0 (&group->mark_mutex){+.+.}-{3:3}:
> check_prev_add kernel/locking/lockdep.c:3133 [inline]
> check_prevs_add kernel/locking/lockdep.c:3252 [inline]
> validate_chain+0x18e0/0x5900 kernel/locking/lockdep.c:3868
> __lock_acquire+0x137a/0x2040 kernel/locking/lockdep.c:5142
> lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
> __mutex_lock_common kernel/locking/mutex.c:608 [inline]
> __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
> fsnotify_group_lock include/linux/fsnotify_backend.h:270 [inline]
> fsnotify_destroy_mark+0x38/0x3c0 fs/notify/mark.c:578
> fsnotify_destroy_marks+0x14a/0x660 fs/notify/mark.c:934
> fsnotify_inoderemove include/linux/fsnotify.h:264 [inline]
> dentry_unlink_inode+0x2e0/0x430 fs/dcache.c:403
> __dentry_kill+0x20d/0x630 fs/dcache.c:610
> shrink_kill+0xa9/0x2c0 fs/dcache.c:1055
> shrink_dentry_list+0x2c0/0x5b0 fs/dcache.c:1082
> prune_dcache_sb+0x10f/0x180 fs/dcache.c:1163
> super_cache_scan+0x34f/0x4b0 fs/super.c:221
> do_shrink_slab+0x701/0x1160 mm/shrinker.c:435
> shrink_slab+0x1093/0x14d0 mm/shrinker.c:662
> shrink_one+0x43b/0x850 mm/vmscan.c:4815
> shrink_many mm/vmscan.c:4876 [inline]
> lru_gen_shrink_node mm/vmscan.c:4954 [inline]
> shrink_node+0x3799/0x3de0 mm/vmscan.c:5934
> kswapd_shrink_node mm/vmscan.c:6762 [inline]
> balance_pgdat mm/vmscan.c:6954 [inline]
> kswapd+0x1bcd/0x35a0 mm/vmscan.c:7223
> kthread+0x2f0/0x390 kernel/kthread.c:389
> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(fs_reclaim);
> lock(&group->mark_mutex);
> lock(fs_reclaim);
> lock(&group->mark_mutex);
>
> *** DEADLOCK ***
>
> [Analysis]
> The inotify_new_watch() call passes through GFP_KERNEL, use memalloc_nofs_save/
> memalloc_nofs_restore to make sure we don't end up with the fs reclaim dependency.
>
> That any notification group needs to use NOFS allocations to be safe
> against this race so we can just remove FSNOTIFY_GROUP_NOFS and
> unconditionally do memalloc_nofs_save() in fsnotify_group_lock().
>
> Reported-and-tested-by: syzbot+c679f13773f295d2da53@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c679f13773f295d2da53
> Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
> ---
> V1 -> V2: remove FSNOTIFY_GROUP_NOFS in fsnotify_group_lock and unlock
> V2 -> V3: remove nofs_marks_lock and FSNOTIFY_GROUP_NOFS

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

Thanks,
Amir.

>
> fs/nfsd/filecache.c | 2 +-
> fs/notify/dnotify/dnotify.c | 3 +--
> fs/notify/fanotify/fanotify_user.c | 2 +-
> fs/notify/group.c | 11 -----------
> include/linux/fsnotify_backend.h | 10 +++-------
> 5 files changed, 6 insertions(+), 22 deletions(-)
>
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index 24e8f1fbcebb..2bb8465474dc 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -764,7 +764,7 @@ nfsd_file_cache_init(void)
> }
>
> nfsd_file_fsnotify_group = fsnotify_alloc_group(&nfsd_file_fsnotify_ops,
> - FSNOTIFY_GROUP_NOFS);
> + 0);
> if (IS_ERR(nfsd_file_fsnotify_group)) {
> pr_err("nfsd: unable to create fsnotify group: %ld\n",
> PTR_ERR(nfsd_file_fsnotify_group));
> diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
> index 46440fbb8662..d5dbef7f5c95 100644
> --- a/fs/notify/dnotify/dnotify.c
> +++ b/fs/notify/dnotify/dnotify.c
> @@ -406,8 +406,7 @@ static int __init dnotify_init(void)
> SLAB_PANIC|SLAB_ACCOUNT);
> dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
>
> - dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops,
> - FSNOTIFY_GROUP_NOFS);
> + dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops, 0);
> if (IS_ERR(dnotify_group))
> panic("unable to allocate fsnotify group for dnotify\n");
> dnotify_sysctl_init();
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 13454e5fd3fb..9644bc72e457 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -1480,7 +1480,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
>
> /* fsnotify_alloc_group takes a ref. Dropped in fanotify_release */
> group = fsnotify_alloc_group(&fanotify_fsnotify_ops,
> - FSNOTIFY_GROUP_USER | FSNOTIFY_GROUP_NOFS);
> + FSNOTIFY_GROUP_USER);
> if (IS_ERR(group)) {
> return PTR_ERR(group);
> }
> diff --git a/fs/notify/group.c b/fs/notify/group.c
> index 1de6631a3925..18446b7b0d49 100644
> --- a/fs/notify/group.c
> +++ b/fs/notify/group.c
> @@ -115,7 +115,6 @@ static struct fsnotify_group *__fsnotify_alloc_group(
> const struct fsnotify_ops *ops,
> int flags, gfp_t gfp)
> {
> - static struct lock_class_key nofs_marks_lock;
> struct fsnotify_group *group;
>
> group = kzalloc(sizeof(struct fsnotify_group), gfp);
> @@ -136,16 +135,6 @@ static struct fsnotify_group *__fsnotify_alloc_group(
>
> group->ops = ops;
> group->flags = flags;
> - /*
> - * For most backends, eviction of inode with a mark is not expected,
> - * because marks hold a refcount on the inode against eviction.
> - *
> - * Use a different lockdep class for groups that support evictable
> - * inode marks, because with evictable marks, mark_mutex is NOT
> - * fs-reclaim safe - the mutex is taken when evicting inodes.
> - */
> - if (flags & FSNOTIFY_GROUP_NOFS)
> - lockdep_set_class(&group->mark_mutex, &nofs_marks_lock);
>
> return group;
> }
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index 8be029bc50b1..3ecf7768e577 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -217,7 +217,6 @@ struct fsnotify_group {
>
> #define FSNOTIFY_GROUP_USER 0x01 /* user allocated group */
> #define FSNOTIFY_GROUP_DUPS 0x02 /* allow multiple marks per object */
> -#define FSNOTIFY_GROUP_NOFS 0x04 /* group lock is not direct reclaim safe */
> int flags;
> unsigned int owner_flags; /* stored flags of mark_mutex owner */
>
> @@ -268,22 +267,19 @@ struct fsnotify_group {
> static inline void fsnotify_group_lock(struct fsnotify_group *group)
> {
> mutex_lock(&group->mark_mutex);
> - if (group->flags & FSNOTIFY_GROUP_NOFS)
> - group->owner_flags = memalloc_nofs_save();
> + group->owner_flags = memalloc_nofs_save();
> }
>
> static inline void fsnotify_group_unlock(struct fsnotify_group *group)
> {
> - if (group->flags & FSNOTIFY_GROUP_NOFS)
> - memalloc_nofs_restore(group->owner_flags);
> + memalloc_nofs_restore(group->owner_flags);
> mutex_unlock(&group->mark_mutex);
> }
>
> static inline void fsnotify_group_assert_locked(struct fsnotify_group *group)
> {
> WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
> - if (group->flags & FSNOTIFY_GROUP_NOFS)
> - WARN_ON_ONCE(!(current->flags & PF_MEMALLOC_NOFS));
> + WARN_ON_ONCE(!(current->flags & PF_MEMALLOC_NOFS));
> }
>
> /* When calling fsnotify tell it if the data is a path or inode */
> --
> 2.43.0
>