linux-kernel - Re: [3.11-rc1] CONFIG_DEBUG_MUTEXES=y using gcc 3.x makes unbootablekernel.

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Date:	Mon, 09 Sep 2013 14:07:40 +0200
From:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
CC:	imirkin@...m.mit.edu, linux-kernel@...r.kernel.org,
	daniel.vetter@...ll.ch, robdclark@...il.com,
	a.p.zijlstra@...llo.nl, mingo@...nel.org
Subject: Re: [3.11-rc1] CONFIG_DEBUG_MUTEXES=y using gcc 3.x makes unbootablekernel.

Op 09-09-13 13:56, Tetsuo Handa schreef:
> Maarten Lankhorst wrote:
>> Almost correct. I meant passing it as parameter to __mutex_lock_common. Your version will still cause an extra pointless null check in the ww_mutex_lock case.
> Ah, I see.
> ----------
> >From 95f189eb37c25ddf8e48d5dfc2f9f1185c52b6a8 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Mon, 9 Sep 2013 20:48:13 +0900
> Subject: [PATCH] mutex: Avoid gcc version dependent __builtin_constant_p() usage.
>
> Commit 040a0a37 "mutex: Add support for wound/wait style locks" used
> "!__builtin_constant_p(p == NULL)" but gcc 3.x cannot handle such expression
> correctly, leading to boot failure when built with CONFIG_DEBUG_MUTEXES=y.
>
> Fix it by explicitly passing a bool which tells whether p != NULL or not.
>
Yeah looks ok, did you run the selftests from CONFIG_DEBUG_LOCKING_API_SELFTESTS,
with/without CONFIG_PROVE_LOCKING and once more with DEBUG_MUTEXES also unset?

~Maarten
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