From: Peter Zijlstra <peterz@infradead.org>
To: Roman Gushchin <klamm@yandex-team.ru>
Cc: bsegall@google.com, linux-kernel@vger.kernel.org, pjt@google.com,
chris.j.arges@canonical.com, gregkh@linuxfoundation.org
Subject: Re: [PATCH] sched: tg_set_cfs_bandwidth() causes rq->lock deadlock
Date: Mon, 19 May 2014 12:32:47 +0200 [thread overview]
Message-ID: <20140519103247.GX30445@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <87lhu215ky.wl%klamm@yandex-team.ru>
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On Fri, May 16, 2014 at 12:38:21PM +0400, Roman Gushchin wrote:
> I still think, there is a deadlock. I'll try to explain.
> Three CPUs must be involved:
> CPU0 CPU1 CPU2
> take rq->lock period timer fired
> ... take cfs_b lock
> ... ... tg_set_cfs_bandwidth()
> throttle_cfs_rq() release cfs_b lock take cfs_b lock
> ... distribute_cfs_runtime() timer_active = 0
> take cfs_b->lock wait for rq->lock ...
> __start_cfs_bandwidth()
> {wait for timer callback
> break if timer_active == 1}
>
> So, CPU0 and CPU1 are deadlocked.
OK, so can someone explain this ->timer_active thing? esp. what's the
'obvious' difference with hrtimer_active()?
Ideally we'd change the lot to not have this, but if we have to keep it
we'll need to make it lockdep visible because all this stinks
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next prev parent reply other threads:[~2014-05-19 10:32 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-15 16:58 [PATCH] sched: tg_set_cfs_bandwidth() causes rq->lock deadlock Roman Gushchin
2014-05-15 17:43 ` bsegall
2014-05-16 8:38 ` Roman Gushchin
2014-05-16 17:57 ` bsegall
2014-05-19 11:10 ` Roman Gushchin
2014-05-19 17:40 ` bsegall
2014-05-19 10:32 ` Peter Zijlstra [this message]
2014-05-19 11:37 ` Roman Gushchin
2014-05-19 17:35 ` bsegall
2014-05-19 17:30 ` bsegall
2014-05-20 13:15 ` Peter Zijlstra
2014-05-20 14:01 ` Peter Zijlstra
2014-05-20 14:55 ` Peter Zijlstra
2014-05-20 14:21 ` Roman Gushchin
2014-05-20 14:28 ` Peter Zijlstra
2014-05-20 14:34 ` Roman Gushchin
2014-05-20 19:08 ` bsegall
2014-05-21 7:58 ` Peter Zijlstra
2014-05-19 10:40 ` Peter Zijlstra
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