This is a note to let you know that I've just added the patch titled
mqueue: sys_mq_open: do not call mnt_drop_write() if read-only
to the 3.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mqueue-sys_mq_open-do-not-call-mnt_drop_write-if-read-only.patch
and it can be found in the queue-3.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 38d78e587d4960d0db94add518d27ee74bad2301 Mon Sep 17 00:00:00 2001
From: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Date: Fri, 22 Mar 2013 15:04:51 -0700
Subject: mqueue: sys_mq_open: do not call mnt_drop_write() if read-only
From: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
commit 38d78e587d4960d0db94add518d27ee74bad2301 upstream.
mnt_drop_write() must be called only if mnt_want_write() succeeded,
otherwise the mnt_writers counter will diverge.
mnt_writers counters are used to check if remounting FS as read-only is
OK, so after an extra mnt_drop_write() call, it would be impossible to
remount mqueue FS as read-only. Besides, on umount a warning would be
printed like this one:
=====================================
[ BUG: bad unlock balance detected! ]
3.9.0-rc3 #5 Not tainted
-------------------------------------
a.out/12486 is trying to release lock (sb_writers) at:
mnt_drop_write+0x1f/0x30
but there are no more locks to release!
Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: Doug Ledford <dledford@xxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
ipc/mqueue.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -840,7 +840,8 @@ out_putfd:
fd = error;
}
mutex_unlock(&root->d_inode->i_mutex);
- mnt_drop_write(mnt);
+ if (!ro)
+ mnt_drop_write(mnt);
out_putname:
putname(name);
return fd;
Patches currently in stable-queue which might be from vdavydov@xxxxxxxxxxxxx are
queue-3.8/mqueue-sys_mq_open-do-not-call-mnt_drop_write-if-read-only.patch
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