On Fri, 2012-11-02 at 09:34 +0000, James Bottomley wrote: > > Looking at the arch/parisc/kernel/sys_parisc.c implementation of > > get_shared_area(), I do have a concern though. The function basically > > ignores the pgoff argument, so that if one creates a shared mapping of > > pages 0-N of a file, and then a separate shared mapping of pages 1-N > > of that same file, both will have the same cache offset for their > > starting address. > > > > This looks like this would create obvious aliasing issues. Am I > > misreading this ? I can't understand how this could work good enough > > to be undetected, so there must be something I'm missing here ??? > > No, I think it does. > > I also think the pgoff != 0 case is rare, so it doesn't show very often. > To test this, I booted up with a printk for every pgoff != 0 and it > didn't trigger, so it's probably not seen in the ordinary course of > events. I got it to show: Git uses mmap2 with large page offsets. However, it seems to use offsets with a granularity of 16MB which is 4x our aliasing congruency, so an equivalency problem still wouldn't show up. James -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
