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

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Message-ID: <20070314234208.GC1246@kvack.org>
Date:	Wed, 14 Mar 2007 19:42:08 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Davide Libenzi <davidel@...ilserver.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, Mar 14, 2007 at 04:24:54PM -0700, Davide Libenzi wrote:
> Can you point me to a kernel path that ends up calling aio_complete() in a 
> do-not-sleep mode?

If you remove that invariant, then it is very difficult for device drivers 
and other code to make use of aio_complete().

> The offender I see is drivers/usb/gadget/inode.c that calls it with a 
> spinlock held.

Which was from irq context last time I checked.

> The aio_run_iocb function seem to release/reacquire the lock before 
> calling aio_complete().

That implies nothing -- aio_complete() has to acquire ctx_lock and cannot 
be called holding the lock.  Sure, it could probably be split into 
__aio_complete() and have aio_complete() wrap it acquiring the lock.

		-ben
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