linux-kernel - [ 48/50] ipc/sem.c: synchronize the proc interface

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Date:	Wed, 16 Oct 2013 10:45:34 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 48/50] ipc/sem.c: synchronize the proc interface

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Manfred Spraul <manfred@...orfullife.com>

commit d8c633766ad88527f25d9f81a5c2f083d78a2b39 upstream.

The proc interface is not aware of sem_lock(), it instead calls
ipc_lock_object() directly.  This means that simple semop() operations
can run in parallel with the proc interface.  Right now, this is
uncritical, because the implementation doesn't do anything that requires
a proper synchronization.

But it is dangerous and therefore should be fixed.

Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
Cc: Davidlohr Bueso <davidlohr.bueso@...com>
Cc: Mike Galbraith <efault@....de>
Cc: Rik van Riel <riel@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 ipc/sem.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2103,6 +2103,14 @@ static int sysvipc_sem_proc_show(struct
 	struct sem_array *sma = it;
 	time_t sem_otime;
 
+	/*
+	 * The proc interface isn't aware of sem_lock(), it calls
+	 * ipc_lock_object() directly (in sysvipc_find_ipc).
+	 * In order to stay compatible with sem_lock(), we must wait until
+	 * all simple semop() calls have left their critical regions.
+	 */
+	sem_wait_array(sma);
+
 	sem_otime = get_semotime(sma);
 
 	return seq_printf(s,


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