* [PATCH] mqueue: sys_mq_open: do not call mnt_drop_write() if read-only
@ 2013-03-19 9:31 Vladimir Davydov
2013-03-19 21:09 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Vladimir Davydov @ 2013-03-19 9:31 UTC (permalink / raw)
To: Al Viro
Cc: linux-kernel, devel, Doug Ledford, Andrew Morton,
KOSAKI Motohiro, Eric W. Biederman
mnt_drop_write() must be called only if mnt_want_write() succeeded,
otherwise the mnt_writers counter will diverge.
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
---
ipc/mqueue.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index e5c4f60..3953fda 100644
--- 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;
--
1.7.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mqueue: sys_mq_open: do not call mnt_drop_write() if read-only
2013-03-19 9:31 [PATCH] mqueue: sys_mq_open: do not call mnt_drop_write() if read-only Vladimir Davydov
@ 2013-03-19 21:09 ` Andrew Morton
2013-03-19 22:04 ` Vladimir Davydov
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2013-03-19 21:09 UTC (permalink / raw)
To: Vladimir Davydov
Cc: Al Viro, linux-kernel, devel, Doug Ledford, KOSAKI Motohiro,
Eric W. Biederman
On Tue, 19 Mar 2013 13:31:18 +0400 Vladimir Davydov <vdavydov@parallels.com> wrote:
> mnt_drop_write() must be called only if mnt_want_write() succeeded,
> otherwise the mnt_writers counter will diverge.
>
> ...
>
> --- 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;
huh, that's been there for a while. What were the runtime-visible
effects of the bug?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mqueue: sys_mq_open: do not call mnt_drop_write() if read-only
2013-03-19 21:09 ` Andrew Morton
@ 2013-03-19 22:04 ` Vladimir Davydov
0 siblings, 0 replies; 3+ messages in thread
From: Vladimir Davydov @ 2013-03-19 22:04 UTC (permalink / raw)
To: Andrew Morton
Cc: Al Viro, <linux-kernel@vger.kernel.org>,
<devel@openvz.org>,
Doug Ledford, KOSAKI Motohiro, Eric W. Biederman
On Mar 20, 2013, at 1:09 AM, Andrew Morton <akpm@linux-foundation.org>
wrote:
> On Tue, 19 Mar 2013 13:31:18 +0400 Vladimir Davydov <vdavydov@parallels.com> wrote:
>
>> mnt_drop_write() must be called only if mnt_want_write() succeeded,
>> otherwise the mnt_writers counter will diverge.
>>
>> ...
>>
>> --- 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;
>
> huh, that's been there for a while. What were the runtime-visible
> effects of the bug?
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:
[ 194.714880] =====================================
[ 194.719680] [ BUG: bad unlock balance detected! ]
[ 194.724488] 3.9.0-rc3 #5 Not tainted
[ 194.728159] -------------------------------------
[ 194.732958] a.out/12486 is trying to release lock (sb_writers) at:
[ 194.739355] [<ffffffff811b177f>] mnt_drop_write+0x1f/0x30
[ 194.744851] but there are no more locks to release!
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2013-03-19 22:04 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2013-03-19 9:31 [PATCH] mqueue: sys_mq_open: do not call mnt_drop_write() if read-only Vladimir Davydov
2013-03-19 21:09 ` Andrew Morton
2013-03-19 22:04 ` Vladimir Davydov
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