linux-kernel - Re: [PATCH v3] lib: cpu_rmap: avoid flushing all workqueues

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Message-ID: <CAG88wWZw=DCioNPSgRXWARm5hHmsR-K8UKyZQ93UsAYmijcXfw@mail.gmail.com>
Date:	Wed, 2 Jan 2013 13:12:11 -0800
From:	David Decotigny <decot@...glers.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Amir Vadai <amirv@...lanox.com>,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH v3] lib: cpu_rmap: avoid flushing all workqueues

Revising my position: v4 will only have comments update (Ben) and new
cpu_rmap_get inetrnal helper (Josh). IMHO, further API rework
discussed with Ben and Eric ought to be in a later patch, as they
affect drivers.

--
David Decotigny


On Wed, Jan 2, 2013 at 12:34 PM, David Decotigny <decot@...glers.com> wrote:
> Thanks,
>
> I appreciate your review and clarification, as I was afraid there
> could be something I missed. I will send v4 of this patch: an update
> with the cpu_rmap_get helper that Josh suggested and the
> "free_cpu_rmap" alias removed.
>
> Regards,
>
> --
> David Decotigny
>
> On Wed, Jan 2, 2013 at 12:29 PM, Ben Hutchings
> <bhutchings@...arflare.com> wrote:
>> On Sat, 2012-12-29 at 12:36 -0800, Josh Triplett wrote:
>>> On Sat, Dec 29, 2012 at 11:57:09AM -0800, David Decotigny wrote:
>>> > In some cases, free_irq_cpu_rmap() is called while holding a lock
>>> > (eg. rtnl). This can lead to deadlocks, because it invokes
>>> > flush_scheduled_work() which ends up waiting for whole system
>>> > workqueue to flush, but some pending works might try to acquire the
>>> > lock we are already holding.
>>> >
>>> > This commit uses reference-counting to replace
>>> > irq_run_affinity_notifiers(). It also removes
>>> > irq_run_affinity_notifiers() altogether.
>>> >
>>> > Signed-off-by: David Decotigny <decot@...glers.com>
>>>
>>> You might consider adding a cpu_rmap_get to parallel cpu_rmap_put.
>>>
>>> Also, why keep free_cpu_rmap around at this point?  As far as I can
>>> tell, it has no callers.
>>>
>>> Otherwise, this looks good to me.
>>
>> I intended to make cpu_rmap usable independently of IRQ notification,
>> although as you note there have been no other users so far.
>> free_cpu_rmap() is now effectively an alias for cpu_rmap_put(), and the
>> latter *does* have a caller.  So perhaps cpu_rmap_put() should be extern
>> and the alias dropped.
>>
>> Ben.
>>
>> --
>> Ben Hutchings, Staff Engineer, Solarflare
>> Not speaking for my employer; that's the marketing department's job.
>> They asked us to note that Solarflare product names are trademarked.
>>
--
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