linux-kernel - Re: 2.6.27-rc4-git1: Reported regressions from 2.6.26

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Message-Id: <1219625301.13162.2.camel@pasglop>
Date:	Mon, 25 Aug 2008 10:48:21 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Adrian Bunk <bunk@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Natalie Protasevich <protasnb@...il.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: 2.6.27-rc4-git1: Reported regressions from 2.6.26

> Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=11414
> Subject		: Random crashes with 2.6.27-rc3 on PPC
> Submitter	: Michael Buesch <mb@...sch.de>
> Date		: 2008-08-23 14:10 (1 days old)
> References	: http://marc.info/?l=linux-kernel&m=121950076812616&w=4

This appears to be a gcc bug when -fno-omit-stack-pointer is used (which
we mostly don't need on ppc anyway except that another gcc stupidity makes
it mandatory for -pg which ftrace needs).

We're working on a two fold workaround: removing -fno-omit-stack-pointer
in all the cases where we don't really need it, and for when we do (ie,
CONFIG_FTRACE becaues of -pg), using -mno-sched-epilog which seems to
work around it.

The root cause in gcc hasn't been fully identified yet.

Ben.

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