Messages in this thread Patch in this message | | | From | Chengming Zhou <> | Subject | [PATCH] fs/kernfs: Fix lockdep warning in kernfs_active() | Date | Wed, 9 Nov 2022 20:04:15 +0800 |
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syzbot found a lockdep warning in kernfs_find_and_get_node_by_id(), bisected to the commit c25491747b21 ("kernfs: Add KERNFS_REMOVING flags"), which didn't hold kernfs_rwsem before call kernfs_active(kn).
Since kernfs_find_and_get_node_by_id() doesn't have to get active count of kn, only need to get a stable refcount of kn, so it should be enough to just check kn has been KERNFS_ACTIVATED.
Reported-by: syzbot+2fdf66e68f5f882c1074@syzkaller.appspotmail.com Fixes: c25491747b21 ("kernfs: Add KERNFS_REMOVING flags") Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> --- fs/kernfs/dir.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 6acd9c3d4cff..08f0f1570cd7 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -705,7 +705,13 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root, goto err_unlock; } - if (unlikely(!kernfs_active(kn) || !atomic_inc_not_zero(&kn->count))) + /* + * ACTIVATED is protected with kernfs_mutex but it was clear when + * @kn was added to idr and we just wanna see it set. No need to + * grab kernfs_mutex. + */ + if (unlikely(!(kn->flags & KERNFS_ACTIVATED) || + !atomic_inc_not_zero(&kn->count))) goto err_unlock; spin_unlock(&kernfs_idr_lock); -- 2.37.2
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