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Date: Fri, 28 Dec 2012 17:01:13 +0800
From: Zhouping Liu <zliu@...hat.com>
To: Zlatko Calusic <zlatko.calusic@...on.hr>
CC: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>,
Johannes Weiner <jweiner@...hat.com>, mgorman@...e.de,
hughd@...gle.com, Andrea Arcangeli <aarcange@...hat.com>,
Hillf Danton <dhillf@...il.com>, sedat.dilek@...il.com
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at 0000000000000500
On 12/28/2012 10:45 AM, Zhouping Liu wrote:
>> Thank you for the report Zhouping!
>>
>> Would you be so kind to test the following patch and report results?
>> Apply the patch to the latest mainline.
> Hello Zlatko,
>
> I have tested the below patch(applied it on mainline directly),
> but IMO, I'd like to say it maybe don't fix the issue completely.
Hi Zlatko,
I re-tested it on another machine, which has 60+ Gb RAM and 4 numa nodes,
without your patch, it's easy to reproduce the 'NULL pointer' error,
after applying your patch, I couldn't reproduce the issue any more.
depending on the above, it implied that your patch fixed the issue.
but in my last mail, I tested it on two machines, which caused hung task
with your patch,
so I'm confusing is it your patch block some oom-killer performance? if
it's not, your patch is good for me.
Thanks,
Zhouping
>
> run the reproducer[1] on two machine, one machine has 2 numa nodes(8Gb RAM),
> another one has 4 numa nodes(8Gb RAM), then the system hung all the time, such as the dmesg log:
>
> [ 713.066937] Killed process 6085 (oom01) total-vm:18880768kB, anon-rss:7915612kB, file-rss:4kB
> [ 959.555269] INFO: task kworker/13:2:147 blocked for more than 120 seconds.
> [ 959.562144] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 1079.382018] INFO: task kworker/13:2:147 blocked for more than 120 seconds.
> [ 1079.388872] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 1199.209709] INFO: task kworker/13:2:147 blocked for more than 120 seconds.
> [ 1199.216562] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 1319.036939] INFO: task kworker/13:2:147 blocked for more than 120 seconds.
> [ 1319.043794] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 1438.864797] INFO: task kworker/13:2:147 blocked for more than 120 seconds.
> [ 1438.871649] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 1558.691611] INFO: task kworker/13:2:147 blocked for more than 120 seconds.
> [ 1558.698466] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> ......
>
> I'm not sure whether it's your patch triggering the hung task or not, but reverted cda73a10eb3,
> the reproducer(oom01) can PASS without both 'NULL pointer dereference at 0000000000000500' and hung task issues.
>
> but some time, it's possible that the reproducer(oom01) cause hung task on a box with large RAM(100Gb+), so I can't judge it...
>
> Thanks,
> Zhouping
>
>> Thanks,
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 23291b9..e55ce55 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2564,6 +2564,7 @@ static bool prepare_kswapd_sleep(pg_data_t
>> *pgdat, int order, long remaining,
>> static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>> int *classzone_idx)
>> {
>> + bool pgdat_is_balanced = false;
>> struct zone *unbalanced_zone;
>> int i;
>> int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
>> @@ -2638,8 +2639,11 @@ loop_again:
>> zone_clear_flag(zone, ZONE_CONGESTED);
>> }
>> }
>> - if (i < 0)
>> +
>> + if (i < 0) {
>> + pgdat_is_balanced = true;
>> goto out;
>> + }
>>
>> for (i = 0; i <= end_zone; i++) {
>> struct zone *zone = pgdat->node_zones + i;
>> @@ -2766,8 +2770,11 @@ loop_again:
>> pfmemalloc_watermark_ok(pgdat))
>> wake_up(&pgdat->pfmemalloc_wait);
>>
>> - if (pgdat_balanced(pgdat, order, *classzone_idx))
>> + if (pgdat_balanced(pgdat, order, *classzone_idx)) {
>> + pgdat_is_balanced = true;
>> break; /* kswapd: all done */
>> + }
>> +
>> /*
>> * OK, kswapd is getting into trouble. Take a nap, then take
>> * another pass across the zones.
>> @@ -2775,7 +2782,7 @@ loop_again:
>> if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
>> if (has_under_min_watermark_zone)
>> count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
>> - else
>> + else if (unbalanced_zone)
>> wait_iff_congested(unbalanced_zone, BLK_RW_ASYNC, HZ/10);
>> }
>>
>> @@ -2788,9 +2795,9 @@ loop_again:
>> if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
>> break;
>> } while (--sc.priority >= 0);
>> -out:
>>
>> - if (!pgdat_balanced(pgdat, order, *classzone_idx)) {
>> +out:
>> + if (!pgdat_is_balanced) {
>> cond_resched();
>>
>> try_to_freeze();
>>
>> --
>> Zlatko
>>
>> --
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