linux-kernel - Re: [PATCH][RFC] AIO: always reinitialize iocb->ki_run_list at the end of aio_run

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Date:	Thu, 24 Jun 2010 21:31:21 +0400
From:	Sergey Temerkhanov <temerkhanov@...ronik.ru>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Sergey Temerkhanov <temerkhanov@...dex.ru>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-aio" <linux-aio@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Zach Brown <zach.brown@...cle.com>,
	Suparna Bhattacharya <suparna@...ibm.com>
Subject: Re: [PATCH][RFC] AIO: always reinitialize iocb->ki_run_list at the end of aio_run_iocb()

On Wednesday 02 June 2010 01:14:48 Jeff Moyer wrote:
> Sergey Temerkhanov <temerkhanov@...dex.ru> writes:
> > On Wednesday 26 May 2010 23:38:35 Jeff Moyer wrote:
> > ...
> OK, you tried two aio_put_req() calls, and it worked, but you thought
> 
> maybe it wasn't the right approach.  So:
> > So, I've tried another approach (hack) - requeue the kiocb with
> > kick_iocb() before calling aio_put_req() in the ki_cancel() callback
> > (that's because aio_run_iocb() takes some special actions for the
> > canceled kiocbs). And I've found out that kick_iocb() fails because
> > aio_run_iocb() does this:
> > 	iocb->ki_run_list.next = iocb->ki_run_list.prev = NULL;
> > and only reinitializes iocb->ki_run_list when iocb->ki_retry() returns
> > -EIOCBRETRY but kick_iocb() is exported and looks like intended for usage
> > (though not recommended).
> 
> You implemented this other hack, and ran into troubles, so you're
> modifying the aio core to fix it.  Am I wrong in concluding that if you
> keep your first solution above, you no longer need this second?

Well, let's forget the reference counting for now since failing kick_iocb() is 
generally not related to it. I've just described how I've run into it 
- I could run into it somehow else.

The problem with kick_iocb() is exactly as this: If retry() method 
returns -EIOCBQUEUED to aio_run_iocb() then any subsequent call to 
kick_iocb() results in failure. Is it expected behavior?

> 
> You may also find the following an interesting read:
> 
> http://permalink.gmane.org/gmane.linux.kernel.aio.general/2571
> 
> Cheers,
> Jeff
> 


-- 
Regards, Sergey Temerkhanov,
Cifronic ZAO
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