linux-kernel - Re: RCU bug with v3.17-rc3 ?

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Date:	Fri, 10 Oct 2014 22:40:43 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Nathan Lynch <Nathan_Lynch@...tor.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Felipe Balbi <balbi@...com>, Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Tony Lindgren <tony@...mide.com>,
	Linux USB Mailing List <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	josh@...htriplett.org, Rabin Vincent <rabin@....in>,
	Alan Stern <stern@...land.harvard.edu>,
	Johannes Weiner <hannes@...xchg.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux ARM Kernel Mailing List 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: RCU bug with v3.17-rc3 ?

On 10/10/2014 09:44 PM, Nathan Lynch wrote:
> On 10/10/2014 11:25 AM, Russell King - ARM Linux wrote:
>>
>> Right, so GCC 4.8.{1,2} are totally unsuitable for kernel building (and
>> it seems that this has been known about for some time.)
> 
> Looking at http://gcc.gnu.org/PR58854 it seems that all 4.8.x for x < 3
> are affected, as well as 4.9.0.
> 
>> We can blacklist these GCC versions quite easily.  We already have GCC
>> 3.3 blacklisted, and it's trivial to add others.  I would want to include
>> some proper details about the bug, just like the other existing entries
>> we already have in asm-offsets.c, where we name the functions that the
>> compiler is known to break where appropriate.
> 
> Before blacklisting anything, it's worth considering that simple version
> checks would break existing pre-4.8.3 compilers that have been patched
> for PR58854.  It looks like Yocto and Buildroot issued releases with
> patched 4.8.2 compilers well before the (fixed) 4.8.3 release.  I think
> the most we can reasonably do without breaking some correctly-behaving
> toolchains is to emit a warning.

Providing a manual switch to override blacklisting is way more sane
than a build warning that no one's looking at.

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