linux-kernel - Re: spinlock in completion_done() (was: Re: Async resume patch (was: Re: [GIT PULL] PM updates for 2.6.33))

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Date:	Wed, 9 Dec 2009 10:29:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	David Chinner <david@...morbit.com>,
	Lachlan McIlroy <lachlan@....com>
Subject: Re: spinlock in completion_done() (was: Re: Async resume patch (was:
 Re: [GIT PULL] PM updates for 2.6.33))


* Rafael J. Wysocki <rjw@...k.pl> wrote:

> On Tuesday 08 December 2009, Alan Stern wrote:
> > On Tue, 8 Dec 2009, Rafael J. Wysocki wrote:
> > 
> > > BTW, is there a good reason why completion_done() doesn't use spin_lock_irqsave
> > > and spin_unlock_irqrestore?  complete() and complete_all() use them, so why not
> > > here?
> > 
> > And likewise in try_wait_for_completion().  It looks like a bug.  Maybe 
> > these routines were not intended to be called with interrupts disabled, 
> > but that requirement doesn't seem to be documented.  And it isn't a 
> > natural requirement anyway.
> 
> OK, let's ask Ingo about that.
> 
> Ingo, is there any particular reason why completion_done() and
> try_wait_for_completion() don't use spin_lock_irqsave() and
> spin_unlock_irqrestore()?

that's a bug that should be fixed - all the wakeup side (and atomic) 
variants of completetion API should be irq safe.

It appears that these new completion APIs were added via the XFS tree 
about a year ago:

  39d2f1a: [XFS] extend completions to provide XFS object flush requirements

Please Cc: scheduler folks to all scheduler patches.

	Ingo
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