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From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Wanpeng Li <wanpengli@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH] sched/vtime: Fix guest/system mis-accounting on task switch
Date: Thu, 26 Sep 2019 10:14:00 +0200	[thread overview]
Message-ID: <20190926081400.GH4553@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190925214242.21873-1-frederic@kernel.org>

On Wed, Sep 25, 2019 at 11:42:42PM +0200, Frederic Weisbecker wrote:
> vtime_account_system() assumes that the target task to account cputime
> to is always the current task. This is most often true indeed except on
> task switch where we call:
> 
> 	vtime_common_task_switch(prev)
> 		vtime_account_system(prev)
> 
> Here prev is the scheduling-out task where we account the cputime to. It
> doesn't match current that is already the scheduling-in task at this
> stage of the context switch.
> 
> So we end up checking the wrong task flags to determine if we are
> accounting guest or system time to the previous task.
> 
> As a result the wrong task is used to check if the target is running in
> guest mode. We may then spuriously account or leak either system or
> guest time on task switch.
> 
> Fix this assumption and also turn vtime_guest_enter/exit() to use the
> task passed in parameter as well to avoid future similar issues.
> 
> Fixes: 2a42eb9594a1 ("sched/cputime: Accumulate vtime on top of nsec clocksource")
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Ingo Molnar <mingo@kernel.org>

Thanks!

  reply	other threads:[~2019-09-26  8:14 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-25 21:42 [PATCH] sched/vtime: Fix guest/system mis-accounting on task switch Frederic Weisbecker
2019-09-26  8:14 ` Peter Zijlstra [this message]
2019-10-09 12:59 ` [tip: sched/urgent] " tip-bot2 for Frederic Weisbecker
2019-10-09 12:59 ` [tip: sched/core] " tip-bot2 for Frederic Weisbecker

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