[ 3.8.y.z extended stable ] Patch "CIFS: Fix a deadlock when a file is reopened" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    CIFS: Fix a deadlock when a file is reopened

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 582fdbaaadcf6981f834c0a7d30ca2e16c8791df Mon Sep 17 00:00:00 2001
From: Pavel Shilovsky <pshilovsky at samba.org>
Date: Thu, 11 Jul 2013 11:17:45 +0400
Subject: CIFS: Fix a deadlock when a file is reopened

commit 689c3db4d57a73bee6c5ad7797fce7b54d32a87c upstream.

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.

Signed-off-by: Pavel Shilovsky <pshilovsky at samba.org>
Acked-by: Jeff Layton <jlayton at redhat.com>
Signed-off-by: Steve French <smfrench at gmail.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/cifs/file.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 1d93ee8..ae62632 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -551,11 +551,10 @@ 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;
 	}

@@ -566,7 +565,7 @@ 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;
 }

--
1.8.1.2