Re: aio_down() patch series -- cancellation support added

Re: aio_down() patch series -- cancellation support added

[Benjamin LaHaise]

Add linux-kernel to the Cc list...

On Mon, Jun 20, 2005 at 05:38:35PM -0400, Benjamin LaHaise wrote:
> Hello all,
> 
> The patch series at http://www.kvack.org/~bcrl/patches/aio-2.6.12-A1/ 
> now adds support for cancellation of an aio_down() operation.  The 
> races should be correctly handled by introducing per-kiocb locking 
> that serialises ->ki_cancel() and ->ki_retry().  The interesting patch 
> additions are 40_lock_kiocb 50_aio_down_cancel.diff.  Comments?
> 
> 		-ben
> -- 
> "Time is what keeps everything from happening all at once." -- John Wheeler
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-- 
"Time is what keeps everything from happening all at once." -- John Wheeler

Re: aio_down() patch series -- cancellation support added

[Suparna Bhattacharya]

On Mon, Jun 20, 2005 at 05:46:14PM -0400, Benjamin LaHaise wrote:
> Add linux-kernel to the Cc list...
> 
> On Mon, Jun 20, 2005 at 05:38:35PM -0400, Benjamin LaHaise wrote:
> > Hello all,
> > 
> > The patch series at http://www.kvack.org/~bcrl/patches/aio-2.6.12-A1/ 
> > now adds support for cancellation of an aio_down() operation.  The 
> > races should be correctly handled by introducing per-kiocb locking 
> > that serialises ->ki_cancel() and ->ki_retry().  The interesting patch 
> > additions are 40_lock_kiocb 50_aio_down_cancel.diff.  Comments?
> > 
> > 		-ben
> > -- 

One quick question.
Since lock_kiocb() may block, does that mean that the aio worker thread
could be put to sleep while an iocb cancellation is in progress, even though
there may be other iocbs/ioctx's to process ?

Looking at the rest a little more closely in terms of how everything
will fit together, a few questions come to mind - need to think
about it a little more. I guess the main reason you need the aio_down_wait
callback is to make sure the semaphore is grabbed right in the context
of the wakeup rather than at retry time, is that correct ?

Regards
Suparna

-- 
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Lab, India

Re: aio_down() patch series -- cancellation support added

[Benjamin LaHaise]

On Thu, Jun 23, 2005 at 06:59:26PM +0530, Suparna Bhattacharya wrote:
> One quick question.
> Since lock_kiocb() may block, does that mean that the aio worker thread
> could be put to sleep while an iocb cancellation is in progress, even though
> there may be other iocbs/ioctx's to process ?

It's mostly to deal with the case in the other direction: an iocb that is 
in the process of being cancelled somehow needs to block any retries from 
occurring.  Likewise, if a retry was in progress, the cancellation needs 
to be blocked until that retry is complete.  It should be sufficiently 
rare that it's not a problem, but we may have to revisit the issue as more 
cancel methods get written.

> Looking at the rest a little more closely in terms of how everything
> will fit together, a few questions come to mind - need to think
> about it a little more. I guess the main reason you need the aio_down_wait
> callback is to make sure the semaphore is grabbed right in the context
> of the wakeup rather than at retry time, is that correct ?

Yes, that way the retry method is only called if it will make progress, 
and we will not have a thundering herd problem.  I'm debugging the changes 
needed to implement async pipes using aio_down(), and the patch so far 
looks pretty straightforward.

		-ben
-- 
"Time is what keeps everything from happening all at once." -- John Wheeler