On Mon, 2007-05-28 at 16:39 +0200, Lennert Buytenhek wrote:
> On Mon, May 28, 2007 at 09:17:55AM -0500, James Bottomley wrote:
>
> > > > Ok, output on parisc is:
> > > >
> > > > [EMAIL PROTECTED]:~$ ./a.out
> > > > firstfirstfirst
> > > > firstfirstfirst
> > > > secondsecondsec
> > > >
> > > > Which is correct. It remains correct even if I drop the msync().
> > >
> > > With Lennert's new program, I get mostly:
> > >
> > > firstfirstfirst
> > > firstfirstfirst
> > > firstfirstfirst
> > >
> > > but occasionally:
> > >
> > > firstfirstfirst
> > > firstfirstfirst
> > > secondsecondsec
> > >
> > > However, if I open code the memcpy() in the MAPREAD to copy one word
> > > at a time, then I reliably get the "secondsecondsec" line. But if I
> > > convert the memcpy() in MAPWRITE in the same way, I'm back to mostly
> > > getting the failure with the occasional success. Utterly confused.
> > >
> > > Unless someone's got a theory, I'm stumped.
> >
> > I think you're not flushing correctly in munmap() ... but I'm not sure
> > the linux API actually requires this.
>
> Having to (conditionally) invalidate the kernel direct mapping for
> every userland page we unmap would kind of suck..
Lets just verify it is a stale kernel mapping first. Try this patch: it
will cohere the kernel aliases but not the user ones, so if the problem
goes away its definitely a stale kernel alias rather than a dirty user
one. Actually, I can't find a patch ... what I want is a
flush_kernel_dcache_page() before
if (mapping_writably_mapped(mapping))
flush_dcache_page(page);
But arm doesn't seem to implement the API ... you must have some
equivalent, though, if you can find it ... I think it's
__cpuc_coherent_kern_range(lowmem_page_address(page),
lowmem_page_address(page)+PAGE_SIZE);
But I'm not an arm expert.
James
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