linux-kernel - Re: [PATCH] fs: fput() can be called from interrupt context

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Date:	Fri, 13 Mar 2009 15:34:05 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Moyer <jmoyer@...hat.com>, Avi Kivity <avi@...hat.com>,
	linux-aio <linux-aio@...ck.org>, zach.brown@...cle.com,
	Benjamin LaHaise <bcrl@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] fs: fput() can be called from interrupt context

On Thu, 12 Mar 2009, Davide Libenzi wrote:

> On Wed, 11 Mar 2009, Andrew Morton wrote:
> 
> > > Take the time to check how fs/aio.c handle the fput(req->ki_filp) case
> > > (or read my 2nd patch, it should spot the thing)
> > 
> > Well yes, a kludge like that seems a bit safer.
> > 
> > It's somewhat encouraging that we're apparently already doing fput()
> > from within keventd (although how frequently?).  There might be
> > problems with file locking, security code, etc from doing fput() from
> > an unexpected thread.  And then there are all the usual weird problem
> > with using the keventd queues which take a long time to get discovered.
> 
> Would it be a huge problem, performance-wise, to stop making ->f_count 
> tricks in __aio_put_req, and always offload to fput_work the task of 
> releasing the requests?
> If that's a huge problem, IMO the lower impact fix would be to use 
> aio_fput_routine to loop into a second list, releasing the eventual 
> eventfd file*. There's no need, IMO, to turn the whole fput() into 
> IRQ-callable just for this case, when we can contain it into the 
> particular KAIO+eventfd usage.

Eric, are you working on this or should I? I missed where the conversation 
between you and Andrew is, at this point, WRT this issue.


- Davide


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