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SubjectRe: BUG: unable to handle kernel NULL pointer dereference at 0000000000000500
On 26.12.2012 12:22, Zhouping Liu wrote:
> Hello everyone,
>
> The latest mainline(637704cbc95c) would trigger the following error when the system was under
> some pressure condition(in my testing, I used oom01 case inside LTP test suite to trigger the issue):
>
> [ 5462.920151] BUG: unable to handle kernel NULL pointer dereference at 0000000000000500
> [ 5462.927991] IP: [<ffffffff811542d9>] wait_iff_congested+0x59/0x140
> [ 5462.934176] PGD 0
> [ 5462.936191] Oops: 0000 [#2] SMP
> [ 5462.939428] Modules linked in: lockd sunrpc iptable_mangle ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tabled
> [ 5462.984261] CPU 13
> [ 5462.986184] Pid: 117, comm: kswapd3 Tainted: G D 3.8.0-rc1+ #1 Dell Inc. PowerEdge M905/0D413F
> [ 5462.995814] RIP: 0010:[<ffffffff811542d9>] [<ffffffff811542d9>] wait_iff_congested+0x59/0x140
> [ 5463.004411] RSP: 0018:ffff88007c97fd48 EFLAGS: 00010202
> [ 5463.009701] RAX: 0000000000000001 RBX: 0000000000000064 RCX: 0000000000000001
> [ 5463.016818] RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000000
> [ 5463.023926] RBP: ffff88007c97fd98 R08: 0000000000000000 R09: ffff88022ffd9d80
> [ 5463.031033] R10: 0000000000003189 R11: 0000000000000000 R12: 00000001004ee87e
> [ 5463.038140] R13: 0000000000000002 R14: 0000000000000000 R15: ffff88022ffd9000
> [ 5463.045258] FS: 00007f3e570de740(0000) GS:ffff88022fcc0000(0000) knlGS:0000000000000000
> [ 5463.053317] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [ 5463.059041] CR2: 0000000000000500 CR3: 00000000018dc000 CR4: 00000000000007e0
> [ 5463.066157] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 5463.073276] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [ 5463.080400] Process kswapd3 (pid: 117, threadinfo ffff88007c97e000, task ffff88007c981970)
> [ 5463.088633] Stack:
> [ 5463.090646] ffff88007c97fd98 0000000000000000 ffff88007c981970 ffffffff81086080
> [ 5463.098090] ffff88007c97fd68 ffff88007c97fd68 ffff88022ffd9d80 0000000000000002
> [ 5463.105527] 0000000000000002 0000000000000000 ffff88007c97feb8 ffffffff8114b0e3
> [ 5463.112998] Call Trace:
> [ 5463.115446] [<ffffffff81086080>] ? wake_up_bit+0x40/0x40
> [ 5463.120826] [<ffffffff8114b0e3>] kswapd+0x6c3/0xa50
> [ 5463.125775] [<ffffffff8114aa20>] ? zone_reclaim+0x270/0x270
> [ 5463.131415] [<ffffffff81085680>] kthread+0xc0/0xd0
> [ 5463.136278] [<ffffffff810855c0>] ? kthread_create_on_node+0x120/0x120
> [ 5463.142786] [<ffffffff8160a0ac>] ret_from_fork+0x7c/0xb0
> [ 5463.148166] [<ffffffff810855c0>] ? kthread_create_on_node+0x120/0x120
> [ 5463.154668] Code: 4e 6d 88 00 48 c7 45 b8 00 00 00 00 48 83 c0 18 48 c7 45 c8 80 60 08 81 48 89 45 d0 48 89 45 d8 8b 04 b5 a0 9a cd 81 85 c0 74 0f <48> 8b 87 00 05 00 00 a8 04 0f 85 98 00 00 00 e8 b3 c3
> [ 5463.174097] RIP [<ffffffff811542d9>] wait_iff_congested+0x59/0x140
> [ 5463.180352] RSP <ffff88007c97fd48>
> [ 5463.183824] CR2: 0000000000000500
> [ 5463.203717] ---[ end trace 9ff4ff9087c13a36 ]---
>
> I attached the config file, hope it can make some help.
>
> Thanks,
> Zhouping
>

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.

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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