diff options
| author | Conor Kotwasinski <conorkotwasinski2024@u.northwestern.edu> | 2026-04-16 09:43:15 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-05-22 13:25:41 +0200 |
| commit | 0fdde3f2aeadcf8d090ee3edee0aad73fb91f690 (patch) | |
| tree | ba318393c5a6cec2c183012504431fb5065e5cad | |
| parent | 454257f6d124a92342dcbb7710c03dd6ef96c731 (diff) | |
| download | linux-next-history-0fdde3f2aeadcf8d090ee3edee0aad73fb91f690.tar.gz | |
kernfs: fix suspicious RCU usage in kernfs_put()
Commit 741c10b096bc ("kernfs: Use RCU to access kernfs_node::name.")
converted the WARN_ONCE() in kernfs_put() to read kn->name and
parent->name via rcu_dereference(), but kernfs_put() has callers that
hold neither kernfs_rwsem nor the RCU read lock. The inode eviction
path driven by memory reclaim is one such case:
kernfs_put+0x53/0x60 fs/kernfs/dir.c:602
evict+0x3c2/0xad0 fs/inode.c:846
iput_final fs/inode.c:1966 [inline]
iput.part.0+0x605/0xf50 fs/inode.c:2015
iput+0x35/0x40 fs/inode.c:1981
dentry_unlink_inode+0x2a1/0x490 fs/dcache.c:467
__dentry_kill+0x1d0/0x600 fs/dcache.c:670
shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1174
prune_dcache_sb+0xea/0x150 fs/dcache.c:1256
super_cache_scan+0x328/0x550 fs/super.c:223
...
kswapd+0x556/0xba0 mm/vmscan.c:7343
lockdep complains with "suspicious RCU usage" whenever the WARN
fires from such a context.
Wrap the rcu_dereference() calls in an RCU read-side critical section.
Gate on the active-ref check so the lock is only taken when the WARN
is about to fire.
Note that this does not address the underlying imbalance in
kn->active that triggers the WARN.
Fixes: 741c10b096bc ("kernfs: Use RCU to access kernfs_node::name.")
Reported-by: syzbot+0dfe499ea713e0a15bec@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0dfe499ea713e0a15bec
Signed-off-by: Conor Kotwasinski <conorkotwasinski2024@u.northwestern.edu>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://patch.msgid.link/20260416134315.1474726-1-conorkotwasinski2024@u.northwestern.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/kernfs/dir.c | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 4f9ade82b08ab..e88b71607f1e5 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -597,10 +597,13 @@ void kernfs_put(struct kernfs_node *kn) */ parent = kernfs_parent(kn); - WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS, - "kernfs_put: %s/%s: released with incorrect active_ref %d\n", - parent ? rcu_dereference(parent->name) : "", - rcu_dereference(kn->name), atomic_read(&kn->active)); + if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS) { + guard(rcu)(); + WARN_ONCE(1, + "kernfs_put: %s/%s: released with incorrect active_ref %d\n", + parent ? rcu_dereference(parent->name) : "", + rcu_dereference(kn->name), atomic_read(&kn->active)); + } if (kernfs_type(kn) == KERNFS_LINK) kernfs_put(kn->symlink.target_kn); |