On Fri, Nov 2, 2012 at 4:08 AM, James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > 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. All right. Thanks for looking it up - I just wasn't sure if my reading of the code was correct (and, I am surprised this isn't more common :) -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- 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
