linux-kernel - Re: [patch] fs: aio fix rcu lookup

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Message-ID: <x49aaiwd6cs.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 19 Jan 2011 14:46:27 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Nick Piggin <npiggin@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] fs: aio fix rcu lookup

Jeff Moyer <jmoyer@...hat.com> writes:

> Jan Kara <jack@...e.cz> writes:
>
>>  But there's the second race I describe making it possible
>> for new IO to be created after io_destroy() has waited for all IO to
>> finish...
>
> Can't that be solved by introducing memory barriers around the accesses
> to ->dead?

Upon further consideration, I don't think so.

Given the options, I think adding the synchronize rcu to the io_destroy
path is the best way forward.  You're already waiting for a bunch of
queued I/O to finish, so there is no guarantee that you're going to
finish that call quickly.

Cheers,
Jeff
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