From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andi Kleen <andi@firstfloor.org>,
Ivo Sieben <meltedpianoman@gmail.com>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
linux-serial@vger.kernel.org, Alan Cox <alan@linux.intel.com>,
Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [REPOST] RFC: sched: Prevent wakeup to enter critical section needlessly
Date: Tue, 9 Oct 2012 17:17:29 +0200 [thread overview]
Message-ID: <20121009151729.GA3521@redhat.com> (raw)
In-Reply-To: <1349792104.7880.41.camel@twins>
On 10/09, Peter Zijlstra wrote:
>
> One thing you might need to consider is the memory ordering, will the
> list_empty -- either careful or not -- observe the right list pointer,
> or could it -- when racing with wait_event()/prepare_to_wait() --
> observe a stale value. Or.. is that all already covered in on the use
> site.
I agree.
Without spin_lock(q->lock) (or some other barriers) wait_event-like
code can miss an event.
wait_event:
prepare_to_wait(wq) // takes wq->lock
if (!CONDITION)
schedule();
Now,
CONDITION = 1;
wake_up(wq);
at least need the full mb() before lits_empty().
Oleg.
next prev parent reply other threads:[~2012-10-09 15:16 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-24 13:06 [PATCH] RFC: sched: Prevent wakeup to enter critical section needlessly Ivo Sieben
2012-09-24 13:06 ` Ivo Sieben
2012-10-09 11:30 ` [REPOST] " Ivo Sieben
2012-10-09 11:30 ` Ivo Sieben
2012-10-09 13:37 ` Andi Kleen
2012-10-09 13:37 ` Andi Kleen
2012-10-09 14:15 ` Peter Zijlstra
2012-10-09 15:17 ` Oleg Nesterov [this message]
2012-10-10 14:02 ` Andi Kleen
2012-10-18 8:30 ` [PATCH-v2] " Ivo Sieben
2012-10-18 8:30 ` Ivo Sieben
2012-10-25 10:12 ` [REPOST-v2] " Ivo Sieben
2012-10-25 10:12 ` Ivo Sieben
2012-11-19 7:30 ` Ivo Sieben
2012-11-19 7:30 ` Ivo Sieben
2012-11-19 10:20 ` Preeti U Murthy
2012-11-19 15:10 ` Oleg Nesterov
2012-11-19 15:34 ` Ivo Sieben
2012-11-19 15:49 ` Oleg Nesterov
2012-11-21 13:03 ` Ivo Sieben
2012-11-21 13:47 ` Alan Cox
2012-11-21 13:58 ` Oleg Nesterov
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