[PATCH 5/5] smb: During umount, flush any pending lease breaks for cached dirs

[Paul Aurich <paul@darkrain42.org>]

*** WORK IN PROGRESS ***

If a lease break is received right as a filesystem is being unmounted,
it's possible for cifs_kill_sb() to race with a queued
smb2_cached_lease_break(). Since the cfid is no longer on the
cfids->entries list, close_all_cached_dirs() cannot drop the dentry,
leading to the unmount to report these BUGs:

BUG: Dentry ffff88814f37e358{i=1000000000080,n=/}  still in use (2) [unmount of cifs cifs]
VFS: Busy inodes after unmount of cifs (cifs)
------------[ cut here ]------------
kernel BUG at fs/super.c:661!

Flush anything in the cifsiod_wq workqueue in close_all_cached_dirs.

Fixes: ebe98f1447bb ("cifs: enable caching of directories for which a lease is held")
Cc: stable@vger.kernel.org
Signed-off-by: Paul Aurich <paul@darkrain42.org>
---
 fs/smb/client/cached_dir.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c
index de1e41abdaf2..931108b3bb4a 100644
--- a/fs/smb/client/cached_dir.c
+++ b/fs/smb/client/cached_dir.c
@@ -482,10 +482,13 @@ void close_all_cached_dirs(struct cifs_sb_info *cifs_sb)
 		list_for_each_entry(cfid, &cfids->entries, entry) {
 			dput(cfid->dentry);
 			cfid->dentry = NULL;
 		}
 	}
+
+	/* Flush any pending lease breaks */
+	flush_workqueue(cifsiod_wq);
 }
 
 /*
  * Invalidate all cached dirs when a TCON has been reset
  * due to a session loss.
-- 
2.45.2