linux-kernel - Re: [PATCH] powerpc: secondary CPUs signal to master before setting active and online (fixes kernel BUG at kernel/smpboot.c:134!)

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Date:	Tue, 9 Dec 2014 12:54:43 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Anton Blanchard <anton@...ba.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	yuyang.du@...el.com, lkp@...org,
	Yuanhan Liu <yuanhan.liu@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Daniel J Blueman <daniel@...ascale.com>,
	subbaram@...eaurora.org,
	Brian Norris <computersforpeace@...il.com>,
	Slava Pestov <sp@...era.io>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>, mpe@...erman.id.au
Subject: Re: [PATCH] powerpc: secondary CPUs signal to master before setting
 active and online (fixes kernel BUG at kernel/smpboot.c:134!)

On Mon, Dec 8, 2014 at 3:58 PM, Anton Blanchard <anton@...ba.org> wrote:
> Hi Ingo,
>
>> At that point I thought the previous task_cpu() was somewhat ingrained
>> in the scheduler and came up with the patch. If not, we could go on a
>> hunt to see what else needs fixing.
>
> I had another look. The scheduled does indeed make assumptions about the
> previous task_cpu, but we have a hammer to fix it up called
> select_fallback_rq.
>
> I annotated select_fallback_rq, and did hit a case where the CPU was
> not active. ppc64 patch below.

Anton, I'll assume I will get this through the usual powerpc pull requests?

> I think x86 have a similar (although harder to hit) issue.

Ingo?

                         Linus
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