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

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Message-ID: <1357158557.3652.42.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Wed, 2 Jan 2013 20:29:17 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Josh Triplett <josh@...htriplett.org>
CC:	David Decotigny <decot@...glers.com>,
	<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

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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