On Thu, Sep 04, 2014 at 05:04:37AM -0400, Sasha Levin wrote: > On 08/29/2014 09:23 PM, Sasha Levin wrote: > > On 08/27/2014 11:26 AM, Mel Gorman wrote: > >> > diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h > >> > index 281870f..ffea570 100644 > >> > --- a/include/asm-generic/pgtable.h > >> > +++ b/include/asm-generic/pgtable.h > >> > @@ -723,6 +723,9 @@ static inline pte_t pte_mknuma(pte_t pte) > >> > > >> > VM_BUG_ON(!(val & _PAGE_PRESENT)); > >> > > >> > + /* debugging only, specific to x86 */ > >> > + VM_BUG_ON(val & _PAGE_PROTNONE); > >> > + > >> > val &= ~_PAGE_PRESENT; > >> > val |= _PAGE_NUMA; > > Triggered again, the first VM_BUG_ON got hit, the second one never did. > > Okay, this bug has reproduced quite a few times since then that I no longer > suspect it's random memory corruption. I'd be happy to try out more debug > patches if you have any leads. > The fact the second one doesn't trigger makes me think that this is not related to how the helpers are called and is instead relating to timing. I tried reproducing this but got nothing after 3 hours. How long does it typically take to reproduce in a given run? You mentioned that it takes a few weeks to hit but maybe the frequency has changed since. I tried todays linux-next kernel but it didn't even boot so next-20140826 to match your original report but got nothing. Can you also send me the config you used in case that's a factor. I had one hunch that this may somehow be related to a collision between pagetable teardown during exit and the scanner but I could not find a way that could actually happen. During teardown there should be only one user of the mm and it can't race with itself. A worse possibility is that somehow the lock is getting corrupted but that's also a tough sell considering that the locks should be allocated from a dedicated cache. I guess I could try breaking that to allocate one page per lock so DEBUG_PAGEALLOC triggers but I'm not very optimistic. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>