linux-kernel - Re: [PATCH 3/2] fix flush_workqueue() vs CPU

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Message-ID: <20070103140459.GA12620@in.ibm.com>
Date:	Wed, 3 Jan 2007 19:34:59 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>, Ingo Molnar <mingo@...e.hu>,
	David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	linux-kernel@...r.kernel.org, dipankar@...ibm.com, vatsa@...ibm.com
Subject: Re: [PATCH 3/2] fix flush_workqueue() vs CPU_DEAD race

Hi Andrew,

Sorry, I am yet to check out Venki's and Oleg's patches as I
just returned from Vacation.

On Tue, Jan 02, 2007 at 04:27:27PM -0800, Andrew Morton wrote:
> 
> I have a mental note that these:
> 
> extend-notifier_call_chain-to-count-nr_calls-made.patch
> extend-notifier_call_chain-to-count-nr_calls-made-fixes.patch
> extend-notifier_call_chain-to-count-nr_calls-made-fixes-2.patch

These patches are needed because they allow us to send out the "failed"
notifications to only those subsystems that received the "prepare"
notifications earlier.

> define-and-use-new-eventscpu_lock_acquire-and-cpu_lock_release.patch
> define-and-use-new-eventscpu_lock_acquire-and-cpu_lock_release-fix.patch

These were posted inorder to have a common place where the subsystems
could lock their per-subsystem hotplug mutexes/semaphore from within the
cpu-hotplug-callback function. Hence they are needed IMO.

> eliminate-lock_cpu_hotplug-in-kernel-schedc.patch
> eliminate-lock_cpu_hotplug-in-kernel-schedc-fix.patch

These patches define and use a mutex to handle cpu-hotplug and eliminate
the use of lock_cpu_hotplug in sched.c. Hence they are still needed.

> handle-cpu_lock_acquire-and-cpu_lock_release-in-workqueue_cpu_callback.patch

Again, this one ensures that workqueue_mutex is taken/released on
CPU_LOCK_ACQUIRE/CPU_LOCK_RELEASE events in the cpuhotplug callback
function. So this one is required, unless it conflicts with what Oleg
has posted. Will check that out tonite.

> 
> should be scrapped.  But really I forget what their status is.  Gautham,
> can you please remind us where we're at?
> 

If all goes fine (w.r.t cpufreq and workqueue), eliminating
lock_cpu_hotplug from kernel/*.c should be relatively easy.<fingers crossed>

Thanks and Regards
gautham.
-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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