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

[Russell King - ARM Linux]

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)?