CIFS: Fix a deadlock when a file is reopened

If we request reading or writing on a file that needs to be
reopened, it causes the deadlock: we are already holding rw
semaphore for reading and then we try to acquire it for writing
in cifs_relock_file. Fix this by acquiring the semaphore for
reading in cifs_relock_file due to we don't make any changes in
locks and don't need a write access.

CC: <stable@vger.kernel.org>
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 1dc9dea2ae70d0506f3112bd13627a2fa0da6028..1e57f36ea1b2f84ac43c486cf6aa9cff4b2280a0 100644 (file)
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -561,11 +561,10 @@ cifs_relock_file(struct cifsFileInfo *cfile)
        struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
        int rc = 0;
 
-       /* we are going to update can_cache_brlcks here - need a write access */
-       down_write(&cinode->lock_sem);
+       down_read(&cinode->lock_sem);
        if (cinode->can_cache_brlcks) {
-               /* can cache locks - no need to push them */
-               up_write(&cinode->lock_sem);
+               /* can cache locks - no need to relock */
+               up_read(&cinode->lock_sem);
                return rc;
        }
 
@@ -576,7 +575,7 @@ cifs_relock_file(struct cifsFileInfo *cfile)
        else
                rc = tcon->ses->server->ops->push_mand_locks(cfile);
 
-       up_write(&cinode->lock_sem);
+       up_read(&cinode->lock_sem);
        return rc;
 }