On Fri, Feb 21, 2014 at 01:43:20AM -0500, Sasha Levin wrote: > On 02/20/2014 10:20 PM, Naoya Horiguchi wrote: > > Hi Sasha, > > > > On Thu, Feb 20, 2014 at 06:47:56PM -0500, Sasha Levin wrote: > >> Hi Naoya, > >> > >> This patch seems to trigger a NULL ptr deref here. I didn't have a change to look into it yet > >> but here's the spew: > > > > Thanks for reporting. > > I'm not sure what caused this bug from the kernel message. But in my guessing, > > it seems that the NULL pointer is deep inside lockdep routine __lock_acquire(), > > so if we find out which pointer was NULL, it might be useful to bisect which > > the proble is (page table walker or lockdep, or both.) > > This actually points to walk_pte_range() trying to lock a NULL spinlock. It happens when we call > pte_offset_map_lock() and get a NULL ptl out of pte_lockptr(). I don't think page->ptl was NULL, because if so we hit NULL pointer dereference outside __lock_acquire() (it's derefered in __raw_spin_lock()). Maybe page->ptl->lock_dep was NULL. I'll digging it more to find out how we failed to set this lock_dep thing. > > BTW, just from curiousity, in my build environment many of kernel functions > > are inlined, so should not be shown in kernel message. But in your report > > we can see the symbols like walk_pte_range() and __lock_acquire() which never > > appear in my kernel. How did you do it? I turned off CONFIG_OPTIMIZE_INLINING, > > but didn't make it. > > I'm really not sure. I've got a bunch of debug options enabled and it just seems to do the trick. > > Try CONFIG_READABLE_ASM maybe? Hmm, it makes no change, can I have your config? Thanks, Naoya -- 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>