Re: Crashes in refresh_zone_stat_thresholds when some nodes have no memory
From: Michal Hocko <mhocko@kernel.org>
Date: 2016-10-03 12:47:21
Also in:
linux-mm, lkml
Subsystem:
memory management, memory management - core, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
[Sorry I have only now noticed this email] On Thu 04-08-16 16:44:10, Paul Mackerras wrote:
It appears that commit 75ef71840539 ("mm, vmstat: add infrastructure
for per-node vmstats", 2016-07-28) has introduced a regression on
machines that have nodes which have no memory, such as the POWER8
server that I use for testing. When I boot current upstream, I get a
splat like this:
[ 1.713998] Unable to handle kernel paging request for data at address 0xff7a10000
[ 1.714164] Faulting instruction address: 0xc000000000270cd0
[ 1.714304] Oops: Kernel access of bad area, sig: 11 [#1]
[ 1.714414] SMP NR_CPUS=2048 NUMA PowerNV
[ 1.714530] Modules linked in:
[ 1.714647] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.7.0-kvm+ #118
[ 1.714786] task: c000000ff0680010 task.stack: c000000ff0704000
[ 1.714926] NIP: c000000000270cd0 LR: c000000000270ce8 CTR: 0000000000000000
[ 1.715093] REGS: c000000ff0707900 TRAP: 0300 Not tainted (4.7.0-kvm+)
[ 1.715232] MSR: 9000000102009033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE,TM[E]> CR: 846b6824 XER: 20000000
[ 1.715748] CFAR: c000000000008768 DAR: 0000000ff7a10000 DSISR: 42000000 SOFTE: 1
GPR00: c000000000270d08 c000000ff0707b80 c0000000011fb200 0000000000000000
GPR04: 0000000000000800 0000000000000000 0000000000000000 0000000000000000
GPR08: ffffffffffffffff 0000000000000000 0000000ff7a10000 c00000000122aae0
GPR12: c000000000a1e440 c00000000fb80000 c00000000000c188 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 c000000000cecad0
GPR24: c000000000d035b8 c000000000d6cd18 c000000000d6cd18 c000001fffa86300
GPR28: 0000000000000000 c000001fffa96300 c000000001230034 c00000000122eb18
[ 1.717484] NIP [c000000000270cd0] refresh_zone_stat_thresholds+0x80/0x240
[ 1.717568] LR [c000000000270ce8] refresh_zone_stat_thresholds+0x98/0x240
[ 1.717648] Call Trace:
[ 1.717687] [c000000ff0707b80] [c000000000270d08] refresh_zone_stat_thresholds+0xb8/0x240 (unreliable)
[ 1.717818] [c000000ff0707bd0] [c000000000a1e4d4] init_per_zone_wmark_min+0x94/0xb0
[ 1.717932] [c000000ff0707c30] [c00000000000b90c] do_one_initcall+0x6c/0x1d0
[ 1.718036] [c000000ff0707cf0] [c000000000d04244] kernel_init_freeable+0x294/0x384
[ 1.718150] [c000000ff0707dc0] [c00000000000c1a8] kernel_init+0x28/0x160
[ 1.718249] [c000000ff0707e30] [c000000000009968] ret_from_kernel_thread+0x5c/0x74
[ 1.718358] Instruction dump:
[ 1.718408] 3fc20003 3bde4e34 3b800000 60420000 3860ffff 3fbb0001 4800001c 60420000
[ 1.718575] 3d220003 3929f8e0 7d49502a e93d9c00 <7f8a49ae> 38a30001 38800800 7ca507b4
It turns out that we can get a pgdat in the online pgdat list where
pgdat->per_cpu_nodestats is NULL. On my machine the pgdats for nodes
1 and 17 are like this. All the memory is in nodes 0 and 16.
How is this possible? setup_per_cpu_pageset does
for_each_online_pgdat(pgdat)
pgdat->per_cpu_nodestats =
alloc_percpu(struct per_cpu_nodestat);
so each online node should have the per_cpu_nodestat allocated.
refresh_zone_stat_thresholds then does for_each_online_pgdat and
for_each_populated_zone also shouldn't give any offline pgdat. Is it
possible that this is yet another manifest of 6aa303defb74 ("mm, vmscan:
only allocate and reclaim from zones with pages managed by the buddy
allocator")? I guess the following should be sufficient?diff --git a/mm/vmstat.c b/mm/vmstat.c
index 73aab319969d..c170932a0101 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c@@ -185,6 +185,9 @@ void refresh_zone_stat_thresholds(void) struct pglist_data *pgdat = zone->zone_pgdat; unsigned long max_drift, tolerate_drift; + if (!managed_zone(zone)) + continue; + threshold = calculate_normal_threshold(zone); for_each_online_cpu(cpu) {
quoted hunk ↗ jump to hunk
With the patch below, the system boots normally. I don't guarantee to have found every place that needs a check, and it may be better to fix this by allocating space for per-cpu statistics on nodes which have no memory rather than checking at each use site. Paul. -------- mm: cope with memoryless nodes not having per-cpu statistics allocated It seems that the pgdat for nodes which have no memory will also have no per-cpu statistics space allocated, that is, pgdat->per_cpu_nodestats is NULL. Avoid crashing on machines which have memoryless nodes by checking for non-NULL pgdat->per_cpu_nodestats. Signed-off-by: Paul Mackerras <redacted> ---diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 6137719..48b2780 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h@@ -184,8 +184,9 @@ static inline unsigned long node_page_state_snapshot(pg_data_t *pgdat, #ifdef CONFIG_SMP int cpu; - for_each_online_cpu(cpu) - x += per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->vm_node_stat_diff[item]; + if (pgdat->per_cpu_nodestats) + for_each_online_cpu(cpu) + x += per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->vm_node_stat_diff[item];
Can we ever hit a pgdat which is not managed? Keeping the rest of the email for reference.
quoted hunk ↗ jump to hunk
if (x < 0) x = 0;diff --git a/mm/vmstat.c b/mm/vmstat.c index 89cec42..d83881e 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c@@ -176,6 +176,10 @@ void refresh_zone_stat_thresholds(void) /* Zero current pgdat thresholds */ for_each_online_pgdat(pgdat) { + if (!pgdat->per_cpu_nodestats) { + pr_err("No nodestats for node %d\n", pgdat->node_id); + continue; + } for_each_online_cpu(cpu) { per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold = 0; }@@ -184,6 +188,10 @@ void refresh_zone_stat_thresholds(void) for_each_populated_zone(zone) { struct pglist_data *pgdat = zone->zone_pgdat; unsigned long max_drift, tolerate_drift; + if (!pgdat->per_cpu_nodestats) { + pr_err("No per cpu nodestats\n"); + continue; + } threshold = calculate_normal_threshold(zone);@@ -701,6 +709,8 @@ static int refresh_cpu_vm_stats(bool do_pagesets) for_each_online_pgdat(pgdat) { struct per_cpu_nodestat __percpu *p = pgdat->per_cpu_nodestats; + if (!p) + continue; for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) { int v;@@ -748,6 +758,8 @@ void cpu_vm_stats_fold(int cpu) for_each_online_pgdat(pgdat) { struct per_cpu_nodestat *p; + if (!pgdat->per_cpu_nodestats) + continue; p = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu); for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) --To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
-- Michal Hocko SUSE Labs