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Re: futex_wake_op deadlock?

To: David Daney <ddaney@avtrex.com>
Subject: Re: futex_wake_op deadlock?
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 20 Nov 2007 19:00:41 +0000
Cc: Kaz Kylheku <kaz@zeugmasystems.com>, linux-mips@linux-mips.org
In-reply-to: <4743279B.7070402@avtrex.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20071119184837.GA12287@linux-mips.org> <DDFD17CC94A9BD49A82147DDF7D545C54DCDE2@exchange.ZeugmaSystems.local> <20071120112051.GB30675@linux-mips.org> <4743279B.7070402@avtrex.com>
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On Tue, Nov 20, 2007 at 10:29:47AM -0800, David Daney wrote:

>> Notice the branch at the end of the fixup code, it goes back to the
>> SC instruction.  The SC instruction took an exception so it will not have
>> changed $1 so the loop will continue endless unless by coincidence the
>> value to be stored from $1 happened to be zero.
>>
>> Obviously this one was MIPS specific and may hit all supported ABIs.  So
>> my initial suspicion this might be the issue David Miller recently
>> discovered in the binary compat code isn't true.  And it's a local DoS
>> probably for all of 2.6.16 and up.
>>
>
> I mostly similar code is in 2.6.15, so I think it is effected as well. 
> 2.6.12 on the other hand doesn't seem to have futex.h

It originally appeared in the lmo kernel for 2.6.14-rc1 and a little
after the 2.6.14 release in kernel.org.

If I say 2.6.16 then it's simply that I don't ever look at anything that
doesn't have a -stable branch.

  Ralf

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