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

From: David Decotigny
Date: Wed Jan 02 2013 - 16:12:49 EST

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@xxxxxxxxxxxx> 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@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>>> 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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