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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Message-Id: <200912092337.52492.rjw@sisk.pl>
Date:	Wed, 9 Dec 2009 23:37:52 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Ingo Molnar <mingo@...e.hu>
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))

On Wednesday 09 December 2009, Ingo Molnar wrote:
> 
> * 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.

If you haven't fixed it locally yet, would you mind me posting a fix?

Rafael
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