linux-kernel - Re: [RFC][PATCH v3 2/6] mm, directio: fix fork vs direct-io race (read(2) side IOW gup(write) side)

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Message-ID: <x49hc0rxg1r.fsf@segfault.boston.devel.redhat.com>
Date:	Tue, 14 Apr 2009 14:10:08 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	Nick Piggin <nickpiggin@...oo.com.au>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, Hugh Dickins <hugh@...itas.com>,
	Zach Brown <zach.brown@...cle.com>,
	Andy Grover <andy.grover@...cle.com>
Subject: Re: [RFC][PATCH v3 2/6] mm, directio: fix fork vs direct-io race (read(2) side IOW gup(write) side)

Andrea Arcangeli <aarcange@...hat.com> writes:

> On Tue, Apr 14, 2009 at 12:45:41PM -0400, Jeff Moyer wrote:
>> So, if you're continuously submitting async read I/O, you will starve
>> out the fork() call indefinitely.  I agree that you want to allow
>
> IIRC rwsem good enough to stop the down_read when a down_write is
> blocked. Otherwise page fault flood in threads would also starve any
> mmap or similar call. Still with this approach fork will start to hang

Really?  I don't actually see that in the code, have I missed it?

Cheers,
Jeff
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