On 26.12.2015 13:09, Mikulas Patocka wrote: >> On Tue, 24 Nov 2015, Helge Deller wrote: >>> * Mikulas Patocka <mpatocka@xxxxxxxxxx>: >>>> On Tue, 24 Nov 2015, Helge Deller wrote: >>>>>> Hi >>>>>> >>>>>> Since the kernel 4.4-rc2 I'm getting frequent boot failures on PA-RISC. >>>>>> When I revert this patchset, the crashes are gone. >>>>> >>>>>> [ 3.296666] CPU(s): 4 out of 4 PA8900 (Shortfin) at 1000.000000 MHz online >>>>> >>>>> Hi Mikulas, >>>>> >>>>> Yes, I've seen this as well. >>>>> It affects only the PA8900 CPUs, while all PA8500-PA8700 machines seem to work fine. >>>>> I do have a temporary 3-line patch to avoid the crashes which I'll push to my tree shortly. >>>>> I'm still investigating why it only affects the PA8900 CPUs, but I assume >>>>> it's related to the cache aliasing of those CPUs. >>>>> I'll keep you updated. >>>>> >>>>> Helge >>>> >>>> The PA-RISC specification doesn't allow aliasing on non-equaivalent >>>> addresses. Can the kernel map a piece of kernel data to other virtual >>>> address? If yes, we can't use big pages to map kernel data. >>> >>> Can you please try the two patches below? >>> The first one disables mapping kernel text/data on huge pages on >>> PA8800/PA8900 CPUs. Patch works for me on my Mako PA8800. >>> >>> Independend of my huge page patch the second patch disables the tlb >>> flush optimization we added earlier. It seems calling flush_tlb_all() >>> doesn't reliably flushes tlbs on all CPUs so it's better to fall back to >>> the loop implementation. >>> >>> Helge >> >> The kernel with these patches works fine so far. >> >> Mikulas > > BTW. I looked at this in arch/parisc/mm/hugetlbpage.c:set_huge_pte_at > "*ptep = entry;" and it seems like a bad bug. PA-RISC doesn't have atomic > instructions to modify page table entries, so it takes spinlock in the TLB > handler and modifies the page table entry non-atomically. If you modify > the page table entry without the spinlock, you may race with TLB handler > on another CPU and your modification may be lost. Right. > The comment says something about double locking on pa_tlb_lock, but > pa_tlb_lock isn't held when that function is called. I have a work-in-progress patch for that in one of my trees, e.g.: http://git.kernel.org/cgit/linux/kernel/git/deller/parisc-linux.git/commit/?h=parisc-next&id=5c76b525cbdb097401f46522b27b1eb6244f34f9 It's lightly tested though. Helge -- 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
