On Fri 03-06-16 11:55:49, Michal Hocko wrote: > On Fri 03-06-16 17:43:47, Sergey Senozhatsky wrote: > > On (06/03/16 09:25), Michal Hocko wrote: > > > > it's quite hard to trigger the bug (somehow), so I can't > > > > follow up with more information as of now. > > > > either I did something very silly fixing up the patch, or the > > patch may be causing general protection faults on my system. > > > > RIP collect_mm_slot() + 0x42/0x84 > > khugepaged > > So is this really collect_mm_slot called directly from khugepaged or is > some inlining going on there? > > > prepare_to_wait_event > > maybe_pmd_mkwrite > > kthread > > _raw_sin_unlock_irq > > ret_from_fork > > kthread_create_on_node > > > > collect_mm_slot() + 0x42/0x84 is > > I guess that the problem is that I have missed that __khugepaged_exit > doesn't clear the cached khugepaged_scan.mm_slot. Does the following on > top fixes that? That wouldn't be sufficient after a closer look. We need to do the same from khugepaged_scan_mm_slot when atomic_inc_not_zero fails. So I guess it would be better to stick it into collect_mm_slot. Thanks for your testing! --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 6574c62ca4a3..0432581fb87c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2011,6 +2011,9 @@ static void collect_mm_slot(struct mm_slot *mm_slot) /* khugepaged_mm_lock actually not necessary for the below */ free_mm_slot(mm_slot); mmdrop(mm); + + if (khugepaged_scan.mm_slot == mm_slot) + khugepaged_scan.mm_slot = NULL; } } -- Michal Hocko 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>