From: bsegall@google.com
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, pjt@google.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/5] sched: Fix cfs_bandwidth misuse of hrtimer_expires_remaining
References: <20131016181548.22647.17161.stgit@sword-of-the-dawn.mtv.corp.google.com>
	<20131016181617.22647.73829.stgit@sword-of-the-dawn.mtv.corp.google.com>
	<20131016184144.GH2675@laptop.programming.kicks-ass.net>
Date: Wed, 16 Oct 2013 12:12:52 -0700
In-Reply-To: <20131016184144.GH2675@laptop.programming.kicks-ass.net> (Peter
	Zijlstra's message of "Wed, 16 Oct 2013 20:41:44 +0200")
Message-ID: <xm2661sxyqq3.fsf@sword-of-the-dawn.mtv.corp.google.com>
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Peter Zijlstra <peterz@infradead.org> writes:

> On Wed, Oct 16, 2013 at 11:16:17AM -0700, Ben Segall wrote:
>> + * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
>> + * hrtimer base being cleared by __hrtimer_start_range_ns. This is possibly
>> + * incorrect if we ever built with CPU_HOTPLUG.
>
> Do clarify; most people build with hotplug enabled; due to wanting
> suspend/resume stuff etc..

Whoops, that comment turned out to be incorrect anyway - I was worried
about migrate_timers, but it is safe as it is. The following should be
accurate:

+ * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
+ * hrtimer base being cleared by __hrtimer_start_range_ns. In the case of
+ * migrate_hrtimers, base is never cleared, so we are fine.
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