Subject: FAILED: patch "[PATCH] smb: client: avoid leaking refcount in" failed to apply to 5.15-stable tree
To: doebel@amazon.de,linkinjeon@kernel.org,pc@manguebit.org
Cc: <stable@vger.kernel.org>
From: <gregkh@linuxfoundation.org>
Date: Wed, 16 Sep 2026 17:44:15 +0100
Message-ID: <2026091615-enchanted-bucktooth-2e30@gregkh>
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The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 9f2e63f1b2d5fc5b5423424902c091123e220e7e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026091615-enchanted-bucktooth-2e30@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:


thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9f2e63f1b2d5fc5b5423424902c091123e220e7e Mon Sep 17 00:00:00 2001
From: Bjoern Doebel <doebel@amazon.de>
Date: Thu, 3 Sep 2026 21:28:58 +0000
Subject: [PATCH] smb: client: avoid leaking refcount in
 cifs_queue_oplock_break()

cifs_queue_oplock_break() unconditionally takes a reference on the
target file before queueing cifs_oplock_break(). Only that work item
decreases the reference counter again.

If another oplock break arrives while that work is still queued,
queue_work() will return false and not queue this second work item. As a
result, we will never reach the point to drop the file reference again
and are leaking this reference. This can be triggered when interacting
with a slow-responding server.

As a result, later unmount operations for this file system will fail with

  BUG: Dentry ... still in use (1) [unmount of cifs cifs]
  VFS: Busy inodes after unmount of cifs (cifs)
  kernel BUG at fs/super.c:777!

Fix this by only incrementing the reference count if the work has been
queued successfully. Taking it after queue_work() is safe because all
three callers hold tcon->open_file_lock across the call and
_cifsFileInfo_put() decrements under that same lock, so a worker that
starts the handler in the window cannot drop the reference before it has
been taken.

Fixes: b98749cac4a69 ("CIFS: keep FileInfo handle live during oplock break")
Cc: stable@vger.kernel.org
Assisted-by: Kiro:claude-opus-5
Signed-off-by: Bjoern Doebel <doebel@amazon.de>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>

diff --git a/fs/smb/client/misc.c b/fs/smb/client/misc.c
index d4db3f91a91f..945194fe7a97 100644
--- a/fs/smb/client/misc.c
+++ b/fs/smb/client/misc.c
@@ -378,10 +378,11 @@ void cifs_queue_oplock_break(struct cifsFileInfo *cfile)
 	 * open_file_lock to enforce the validity of it for the oplock
 	 * break handler. The matching put is done at the end of the
 	 * handler.
+	 *
+	 * Only take a reference if the work is actually queued.
 	 */
-	cifsFileInfo_get(cfile);
-
-	queue_work(cifsoplockd_wq, &cfile->oplock_break);
+	if (queue_work(cifsoplockd_wq, &cfile->oplock_break))
+		cifsFileInfo_get(cfile);
 }
 
 void cifs_done_oplock_break(struct cifsInodeInfo *cinode)