Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vladimir Davydov , Doug Ledford , KOSAKI Motohiro , "Eric W. Biederman" , Al Viro , Andrew Morton , Linus Torvalds Subject: [ 53/98] mqueue: sys_mq_open: do not call mnt_drop_write() if read-only Date: Tue, 26 Mar 2013 15:42:42 -0700 Message-Id: <20130326224248.053323864@linuxfoundation.org> In-Reply-To: <20130326224242.449070940@linuxfoundation.org> References: <20130326224242.449070940@linuxfoundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vladimir Davydov 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 Cc: Doug Ledford Cc: KOSAKI Motohiro Cc: "Eric W. Biederman" Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- 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;