linux-kernel - Re: [PATCH] sched, autogroup: Fix failure when writing to cpu.rt_runtime

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Message-ID: <54D95E3E.20207@huawei.com>
Date:	Tue, 10 Feb 2015 09:26:22 +0800
From:	Zefan Li <lizefan@...wei.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Stefan Bader <stefan.bader@...onical.com>
Subject: Re: [PATCH] sched, autogroup: Fix failure when writing to cpu.rt_runtime_us

> Subject: sched, autogroup: Fix failure to set cpu.rt_runtime_us
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Mon Feb  9 11:53:18 CET 2015
> 
> Because task_group() uses a cache of autogroup_task_group(), whoes
> output depends on sched_class, switching classes can generate
> problems.
> 
> In particular, when started as fair, the cache points to the
> autogroup, so when switching to RT the tg_rt_schedulable() test fails
> for every cpu.rt_{runtime,period}_us change because now the autogroup
> has tasks and no runtime.
> 
> Furthermore, going back to the previous semantics of varying
> task_group() with sched_class has the down-side that the sched_debug
> output varies as well, even though the task really is in the
> autogroup.
> 
> Therefore add an autogroup exception to tg_has_rt_tasks() -- such that
> both (all) task_group() usages in sched/core now have one. And remove
> all the remnants of the variable task_group() output.
> 
> Cc: Mike Galbraith <umgwanakikbuti@...il.com>
> Cc: Stefan Bader <stefan.bader@...onical.com>
> Reported-by: Zefan Li <lizefan@...wei.com>
> Fixes: 8323f26ce342 ("sched: Fix race in task_group()")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Both patches look good to me.

Thanks!

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