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

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Date:	Fri, 13 Mar 2009 23:43:25 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Davide Libenzi <davidel@...ilserver.org>
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

Davide Libenzi a écrit :
> 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.

I wish I could, but I currently have too much stress from my day job.

BTW, I could not produce a crash, so this problem is hypothetic for the moment :)


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