linux-kernel - Re: [PATCH 2/2] ipc/sem.c: move wake_up

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Message-Id: <20100511142149.83bb3538.akpm@linux-foundation.org>
Date:	Tue, 11 May 2010 14:21:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Chris Mason <chris.mason@...cle.com>,
	Zach Brown <zach.brown@...cle.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 2/2] ipc/sem.c: move wake_up_process out of the spinlock
 section

On Wed, 28 Apr 2010 21:06:27 +0200
Manfred Spraul <manfred@...orfullife.com> wrote:

> The wake-up part of semtimedop() consists out of two steps:
> - the right tasks must be identified.
> - they must be woken up.
> 
> Right now, both steps run while the array spinlock is held.
> This patch reorders the code and moves the actual wake_up_process()
> behind the point where the spinlock is dropped.
> 
> The code also moves setting sem->sem_otime to one place: It does not
> make sense to set the last modify time multiple times.

ipc/sem.c: In function 'update_queue':
ipc/sem.c:545: warning: 'retval' may be used uninitialized in this function

which indeed was a bug.

--- a/ipc/sem.c~ipc-semc-move-wake_up_process-out-of-the-spinlock-section-fix-2
+++ a/ipc/sem.c
@@ -542,7 +542,7 @@ static int update_queue(struct sem_array
 	struct list_head *walk;
 	struct list_head *pending_list;
 	int offset;
-	int retval;
+	int retval = 0;
 
 	/* if there are complex operations around, then knowing the semaphore
 	 * that was modified doesn't help us. Assume that multiple semaphores
_

But I worry that the patch which you sent might not have been the one
which you tested.

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