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

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Message-ID: <alpine.DEB.1.10.0903120625340.6040@makko.or.mcafeemobile.com>
Date:	Thu, 12 Mar 2009 06:39:16 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Eric Dumazet <dada1@...mosbay.com>, 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 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.


- Davide


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