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Message-Id: <20221109120415.55759-1-zhouchengming@bytedance.com>
Date: Wed, 9 Nov 2022 20:04:15 +0800
From: Chengming Zhou <zhouchengming@...edance.com>
To: gregkh@...uxfoundation.org, tj@...nel.org
Cc: linux-kernel@...r.kernel.org,
Chengming Zhou <zhouchengming@...edance.com>,
syzbot+2fdf66e68f5f882c1074@...kaller.appspotmail.com
Subject: [PATCH] fs/kernfs: Fix lockdep warning in kernfs_active()
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@...kaller.appspotmail.com
Fixes: c25491747b21 ("kernfs: Add KERNFS_REMOVING flags")
Signed-off-by: Chengming Zhou <zhouchengming@...edance.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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