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Message-ID: <1445226710.15861.28.camel@gmail.com>
Subject: Re: [GIT PULL] workqueue fixes for v4.3-rc5
From: Mike Galbraith <umgwanakikbuti@gmail.com>
Date: Mon, 19 Oct 2015 05:51:50 +0200
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To: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Christoph Lameter <cl@linux.com>, Michal Hocko <mhocko@suse.cz>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Lai Jiangshan <jiangshanlai@gmail.com>, Shaohua Li <shli@fb.com>, linux-mm <linux-mm@kvack.org>

On Wed, 2015-10-14 at 16:24 -0400, Tejun Heo wrote:

> But in terms of API consistency, it sucks to have queue_work()
> guarantee local queueing but not queue_delayed_work().  The ideal
> situation would be updating both so that neither guarantees.

You don't have to change anything to have neither guarantee local
queueing.  Called from a preemptible context, local means any CPU in
->cpus_allowed... which makes WORK_CPU_UNBOUND mean what one would
imagine WORK_CPU_UNBOUND to mean, not bound to any particular cpu.

      sh-16017   3.N.. 1510500545us : queue_work_on: golly, migrated cpu7 -> cpu3 -- target cpu8
      sh-16017   3.N.. 1510500550us : <stack trace>
 => tty_flip_buffer_push
 => pty_write
 => n_tty_write
 => tty_write
 => __vfs_write
 => vfs_write
 => SyS_write
 => entry_SYSCALL_64_fastpath

That was with a udelay(100) prior to disabling interrupts, but that just
makes it easier.

	-Mike

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