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 17:15:30 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Davide Libenzi <davidel@...ilserver.org>
cc:	Benjamin LaHaise <bcrl@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...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, Davide Libenzi wrote:
> >
> > 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?

All of them.

It's called from dio_bio_end_aio(), which is the bi_end_io function for an 
AIO action. Which in turn is called at IO completion time. 

Which is basically _always_ interrupt context.

So you cannot sleep. It's not about holding spinlocks (which it might well 
do as well). It's about a much more fundamental issue: you can only sleep 
in process context, not from interrupts.

		Linus
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