linux-kernel - Re: Crashes with 874bbfe600a6 in 3.18.25

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Date:	Tue, 9 Feb 2016 11:50:24 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Michal Hocko <mhocko@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Petr Mladek <pmladek@...e.com>, Jan Kara <jack@...e.cz>,
	Ben Hutchings <ben@...adent.org.uk>,
	Sasha Levin <sasha.levin@...cle.com>, Shaohua Li <shli@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>,
	Daniel Bilik <daniel.bilik@...system.cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Crashes with 874bbfe600a6 in 3.18.25

Hello,

On Tue, Feb 09, 2016 at 08:39:15AM -0800, Linus Torvalds wrote:
> > A niggling question remaining is when is it gonna be killed?
> 
> It probably should be killed sooner rather than later.
> 
> Just document that if you need something to run on a _particular_ cpu,
> you need to use "schedule_delayed_work_on()" and "add_timer_on()".

I'll queue a patch to put unbound work items on foreign cpus (maybe
every Nth to reduce perf impact).  Wanted to align it to rc1 and then
let it get tested during the devel cycle but missed this window.  It's
a bit late in devel cycle but we can still do it in this cycle.

> The proper fix was 176bed1de5bf, and 874bbfe6 was just wrong.

idk, not doing so is likely to cause subtle bugs which are difficult
to track down.  The problem with -stable is 874bbfe6 being backported
without the matching timer fix.  The right thing to do now probably is
reverting 874bbfe6 for -stable kernels which don't get the timer fix.

Thanks.

-- 
tejun