linux-kernel - Re: alpha: futex regression bisected

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Message-ID: <4F4B273C.9080506@orcon.net.nz>
Date:	Mon, 27 Feb 2012 19:48:28 +1300
From:	Michael Cree <mcree@...on.net.nz>
To:	Richard Henderson <rth@...ddle.net>
CC:	Michel Lespinasse <walken@...gle.com>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
	Matt Turner <mattst88@...il.com>,
	Phil Carmody <ext-phil.2.carmody@...ia.com>
Subject: Re: alpha: futex regression bisected

On 21/02/12 06:28, Richard Henderson wrote:
> On 02/20/12 00:20, Michael Cree wrote:
>> I have noticed some user space problems (pulseaudio crashes in pthread
>> code, glibc/nptl test suite failures, java compiler freezes on SMP alpha
>> systems) that arise when using a 2.6.39 or later kernel on Alpha.
>> Bisecting between 2.6.38 and 2.6.39 (using glibc/nptl test suite as
>> criterion for good/bad kernel) eventually leads to:
>>
>> 8d7718aa082aaf30a0b4989e1f04858952f941bc is the first bad commit
>> commit 8d7718aa082aaf30a0b4989e1f04858952f941bc
>> Author: Michel Lespinasse <walken@...gle.com>
>> Date:   Thu Mar 10 18:50:58 2011 -0800
>>
>>     futex: Sanitize futex ops argument types
>>
>>     Change futex_atomic_op_inuser and futex_atomic_cmpxchg_inatomic
>>     prototypes to use u32 types for the futex as this is the data type the
>>     futex core code uses all over the place.
> 
> 
> futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
>                               u32 oldval, u32 newval)
> ...
>         :       "r"(uaddr), "r"((long)oldval), "r"(newval)
> 
> 
> There is no 32-bit compare instruction.  These are implemented by
> consistently extending the values to a 64-bit type.  Since the
> load instruction sign-extends, we want to sign-extend the other
> quantity as well (despite the fact it's logically unsigned).
> 
> So:
> 
> -        :       "r"(uaddr), "r"((long)oldval), "r"(newval)
> +        :       "r"(uaddr), "r"((long)(int)oldval), "r"(newval)
> 
> should do the trick.

Thanks, that fixes it.  Will you formally submit a patch with commit
message or should I?

You can have at least a Reviewed-by, or even an
Acked-by: Phil Carmody <ext-phil.2.carmody@...ia.com>
who correctly analysed the problem in response to when I suggested the
fix on the debian-alpha email list without explanation.

Cheers
Michael.
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