I-cache/D-cache inconsistency issue with page cache

[mh@glandium.org (Mike Hommey)]

On Sat, Sep 24, 2011 at 10:47:34AM +0100, Russell King - ARM Linux wrote:
> On Sat, Sep 24, 2011 at 11:35:44AM +0200, Mike Hommey wrote:
> > On Fri, Sep 23, 2011 at 08:39:41PM +0100, Russell King - ARM Linux wrote:
> > > On Fri, Sep 23, 2011 at 01:57:21PM +0200, Mike Hommey wrote:
> > > > We've been hitting random crashes at startup with Firefox on tegras
> > > > (under Android), and narrowed it down to a I-cache/D-cache
> > > > inconsistency. A reduced testcase of the issue looks like the following
> > > > (compile as ARM, not Thumb):
> > > 
> > > If you write code at run time, you need to use the sys_cacheflush
> > > API to ensure that it's properly synchronized with the I-cache.  It's
> > > a well known issue, and it applies to any harvard cache structured
> > > CPU which doesn't automatically ensure coherence (which essentially
> > > means all ARMs.)
> > 
> > I do agree it's reasonable to have applications doing that to handle
> > cache synchronization themselves. I wrote such in my message. But I
> > think the kernel should make sure that its page cache is fresh when 
> > it maps it PROT_EXEC. I think it's unreasonable to expect applications
> > doing mmap(PROT_WRITE), inflate, munmap, something, mmap(PROT_EXEC),
> > and execute something there to have to handle cache synchronisation
> > themselves. Especially when it's very CPU dependent (the testcase does
> > not even fail on all ARMs, only tegras, apparently). I'm not talking
> > actual code generation here, which needs platform-dependent behaviour.
> 
> Ok.  Which kernel are you trying this with, and which CPU (please
> confirm Cortex-A9)?

This has been seen on tegra boards under Ubuntu Maverick
(2.6.35.7.something) and under Android (2.6.32.9.something) and on the Asus
Transformer (Android, 2.6.36.3.something). All Cortex-A9 tegras. It has
*not* been reproduced on pandaboards (Cortex-A9 OMAP4430).

Mike