Hi, On 08/03/2017 09:59 AM, Wen Yang wrote: > From: Jiang Biao <jiang.biao2@xxxxxxxxxx> > > When order is -1 or too big, *1UL << order* will be 0, which will > cause divide error like this, > > divide error: 0000 [#1] SMP > Call Trace: > [<ffffffff81168423>] compaction_suitable+0x63/0xc0 > [<ffffffff81168a75>] compact_zone+0x35/0x950 > [<ffffffff811745b5>] ? free_percpu+0xb5/0x140 > [<ffffffff81092b23>] ? schedule_on_each_cpu+0x133/0x160 > [<ffffffff8116949c>] compact_node+0x10c/0x120 > [<ffffffff8116953c>] sysctl_compaction_handler+0x5c/0x90 > [<ffffffff811fa517>] proc_sys_call_handler+0x97/0xd0 > [<ffffffff811fa564>] proc_sys_write+0x14/0x20 > [<ffffffff81187368>] vfs_write+0xb8/0x1a0 > [<ffffffff81187c61>] sys_write+0x51/0x90 > [<ffffffff8100b052>] system_call_fastpath+0x16/0x1b The trace seems to be from an old and non-mainline kernel, as it's the same as you reported here: https://bugzilla.kernel.org/show_bug.cgi?id=196555 In current mainline it seems to me that all callers of __fragmentation_index() will only do so with a valid order. I wouldn't mind making a non-hotpath code more robust, but probably in a more obvious and self-reporting/documented way e.g. something like if (WARN_ON_ONCE(order >= MAX_ORDER)) return 0; > Signed-off-by: Wen Yang <wen.yang99@xxxxxxxxxx> > Reviewed-by: Jiang Biao <jiang.biao2@xxxxxxxxxx> > --- > mm/vmstat.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 76f7367..2f9d012 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -870,6 +870,9 @@ static int __fragmentation_index(unsigned int order, struct contig_page_info *in > { > unsigned long requested = 1UL << order; > > + if (!requested) > + return 0; Seems the indentation is broken here (spaces vs tabs). Thanks, Vlastimil > + > if (!info->free_blocks_total) > return 0; > > -- 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>
