Re: RCU bug with v3.17-rc3 ?

From: Peter Chen
Date: Fri Oct 10 2014 - 23:55:23 EST

On Fri, Oct 10, 2014 at 08:44:33PM -0500, 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 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.

Yocto has PR58854 problem patch.

> Hopefully nobody's still using gcc 4.8 from the Linaro 2013.11 toolchain
> release -- since it's a 4.8.3 prerelease from before the fix was
> committed you'll get GCC_VERSION == 40803 but still generate bad code.
> > However, I'm rather annoyed that there are people here who have known
> > for some time that GCC 4.8.1 and GCC 4.8.2 _can_ lead to filesystem
> > corruption, and have sat on their backsides doing nothing about getting
> > it blacklisted for something like a year.
> Mea culpa, although I hadn't drawn the connection to FS corruption
> reports until now. I have known about the issue for some time, but
> figured the prevalence of the fix in downstream projects largely
> mitigated the issue.
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Best Regards,
Peter Chen
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