Date: Tue, 22 Feb 2005 15:19:38 -0600
To: Jamie Lokier <jamie@shareable.org>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       torvalds@osdl.org, rusty@rustcorp.com.au
Subject: Re: [PATCH/RFC] Futex mmap_sem deadlock
Message-ID: <20050222211938.GB7079@austin.ibm.com>
References: <20050222190646.GA7079@austin.ibm.com> <20050222115503.729cd17b.akpm@osdl.org> <20050222210752.GG22555@mail.shareable.org>
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From: olof@austin.ibm.com (Olof Johansson)
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On Tue, Feb 22, 2005 at 09:07:52PM +0000, Jamie Lokier wrote:
> 
> That won't work because the vma lock must be help between key
> calculation and get_user() - otherwise futex is not reliable.  It
> would work if the futex key calculation was inside the loop.

Sure, but that's still true: It's just that the get_user() is done twice
instead. The semaphore is never released between the key calculation and
the "real" get_user().

> A much simpler solution (and sorry for not offering it earlier,
> because Andrew Morton pointed out this bug long ago, but I was busy), is:

Either way works for me. Andrew/Linus, got a preference? I'll either
post my refresh based on Andrews comments, or code up Jamie's
suggestion.


-Olof
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