[PATCH] smb: client: hold the inode across cifs_oplock_break()

[Joseph Qi <joseph.qi@linux.alibaba.com>]

cifs_oplock_break() drops the handle reference in the middle of the
handler and keeps using cinode afterwards, to send the break
acknowledgment and again in cifs_done_oplock_break().  The reference
cifs_queue_oplock_break() takes is the only pin: the handle holds the
dentry and the dentry is what keeps the inode alive.

When that put is the last reference, the dput() in
cifsFileInfo_put_final() kills an unhashed dentry, drops the last
i_count and evicts the inode, so the rest of the handler runs on an
object whose free is only RCU-deferred.  An unhashed dentry that a
handle still references is an ordinary state: unlinking an open file
leaves the dentry that way, and so does the dcache teardown at unmount.

Take a reference on the inode for the lifetime of the handler and drop
it once the break has been reported.  This also covers the
cifs_get_tlink() failure path, where the put is followed directly by
the out label.

Fixes: b98749cac4a6 ("CIFS: keep FileInfo handle live during oplock break")
Fixes: 23b26f4408ac ("smb: client: avoid leaking refcount when cifs_sb_tlink() fails")
Cc: stable@vger.kernel.org
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
---
 fs/smb/client/file.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index 0767eb5f4687a..2fb52633f57b1 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -3357,6 +3357,14 @@ void cifs_oplock_break(struct work_struct *work)
 	__u64 persistent_fid, volatile_fid;
 	__u16 net_fid;
 
+	/*
+	 * Dropping the handle reference below also drops the dentry
+	 * reference that pins this inode, and cinode is still needed to
+	 * acknowledge the break and to report it as complete.  Hold the inode
+	 * until that is done.
+	 */
+	ihold(inode);
+
 	wait_on_bit(&cinode->flags, CIFS_INODE_PENDING_WRITERS,
 			TASK_UNINTERRUPTIBLE);
 
@@ -3444,6 +3452,7 @@ void cifs_oplock_break(struct work_struct *work)
 	cifs_put_tlink(tlink);
 out:
 	cifs_done_oplock_break(cinode);
+	iput(inode);
 }
 
 #ifdef CONFIG_SWAP
-- 
2.39.3