linux-kernel - Re: [patch 13/13] signalfd/timerfd/asyncfd v5 - KAIO asyncfd support (example/maybe-broken) ...

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Date:	Wed, 14 Mar 2007 16:24:54 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Benjamin LaHaise <bcrl@...ck.org>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Zach Brown <zach.brown@...cle.com>
Subject: Re: [patch 13/13] signalfd/timerfd/asyncfd v5 - KAIO asyncfd support
 (example/maybe-broken) ...

On Wed, 14 Mar 2007, Benjamin LaHaise wrote:

> On Wed, Mar 14, 2007 at 03:19:21PM -0700, Davide Libenzi wrote:
> > +	/*
> > +	 * Check if the user asked us to deliver the result through an
> > +	 * asyncfd. Note that asyncfd_add_results() may sleep. It seems
> > +	 * OK looking at the code, but I'm not sure since inside a USB driver,
> > +	 * aio_complete() is called with a spinlock held. !!CHECK
> > +	 */
> 
> That won't work.  aio_complete() is supposed to be irq safe.

Can you point me to a kernel path that ends up calling aio_complete() in a 
do-not-sleep mode?
The offender I see is drivers/usb/gadget/inode.c that calls it with a 
spinlock held.
The aio_run_iocb function seem to release/reacquire the lock before 
calling aio_complete().



- Davide


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