linux-kernel - Re: [PATCH] sched: tg_set_cfs_bandwidth() causes rq->lock deadlock

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Message-ID: <20140519104011.GY30445@twins.programming.kicks-ass.net>
Date:	Mon, 19 May 2014 12:40:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	bsegall@...gle.com
Cc:	Roman Gushchin <klamm@...dex-team.ru>,
	linux-kernel@...r.kernel.org, pjt@...gle.com,
	chris.j.arges@...onical.com, gregkh@...uxfoundation.org
Subject: Re: [PATCH] sched: tg_set_cfs_bandwidth() causes rq->lock deadlock

On Thu, May 15, 2014 at 10:43:14AM -0700, bsegall@...gle.com wrote:
> I just did notice however that sched_cfs_period_timer reads
> cfs_b->period without any locks, which can in fact race with an update
> to period (and isn't fixed by this patch). If this write doesn't happen
> to be atomic (which is certainly not guaranteed, and is entirely
> plausible on say 32-bit x86, much less other archs), we could read a
> partially written value and move the timer incorrectly. Pulling the
> lock/unlock out of do_sched_cfs_period_timer should fix this easily
> enough.
> 
> unthrottle_offline_cfs_rqs could cause similar issues with its unlocked
> read of quota, and can also be easily fixed.

Ben, will you send patches for this?

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