From: Rik van Riel <riel@redhat.com>
To: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Emmanuel Benisty <benisty.e@gmail.com>,
"Vinod, Chegu" <chegu_vinod@hp.com>,
"Low, Jason" <jason.low2@hp.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
"H. Peter Anvin" <hpa@zytor.com>,
Andrew Morton <akpm@linux-foundation.org>,
aquini@redhat.com, Michel Lespinasse <walken@google.com>,
Ingo Molnar <mingo@kernel.org>,
Larry Woodman <lwoodman@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2 4/4] ipc: sem: do not hold ipc lock more than necessary
Date: Wed, 20 Mar 2013 10:27:57 -0400 [thread overview]
Message-ID: <5149C76D.7090409@redhat.com> (raw)
In-Reply-To: <1362476179.2225.54.camel@buesod1.americas.hpqcorp.net>
On 03/05/2013 04:36 AM, Davidlohr Bueso wrote:
> @@ -1476,8 +1539,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
> queue.sleeper = current;
>
> sleep_again:
> - current->state = TASK_INTERRUPTIBLE;
> sem_unlock(sma);
> + current->state = TASK_INTERRUPTIBLE;
>
> if (timeout)
> jiffies_left = schedule_timeout(jiffies_left);
After modifying my test case to start with a semaphore value of 1 on
every semaphore, and do down followed by up (to have only one process
take each semaphore at a time), I started seeing lost wakeups and the
test case being stuck.
I believe the change above is the cause of that issue.
By unlocking before setting current->state to TASK_INTERRUPTIBLE,
there is a small window where the next lock holder can grab the
lock and wake us up, before we set ourselves to TASK_INTERRUPTIBLE
and go to sleep.
I have reverted your change in my code and am building a test kernel
now.
If things work, I'll clean up the whole patch series for a re-posting
today.
--
All rights reversed
next prev parent reply other threads:[~2013-03-20 14:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-05 9:36 Davidlohr Bueso
2013-03-05 23:11 ` Rik van Riel
2013-03-20 14:27 ` Rik van Riel [this message]
2013-03-20 15:38 ` Rik van Riel
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