At 09/14/2012 04:59 AM, Johannes Weiner Wrote:
> Hi,
>
> On Thu, Sep 13, 2012 at 03:14:28PM +0800, Wen Congyang wrote:
>> root_mem_cgroup->info.nodeinfo is initialized when the system boots.
>> But NODE_DATA(nid) is null if the node is not onlined, so
>> root_mem_cgroup->info.nodeinfo[nid]->zoneinfo[zone].lruvec.zone contains
>> an invalid pointer. If we use numactl to bind a program to the node
>> after onlining the node and its memory, it will cause the kernel
>> panicked:
>
> Is there any chance we could get rid of the zone backpointer in lruvec
> again instead? Adding new nodes is a rare event and so updating every
> single memcg in the system might be just borderline crazy. But can't
> we just go back to passing the zone along with the lruvec down
> vmscan.c paths? I agree it's ugly to pass both, given their
> relationship. But I don't think the backpointer is any cleaner but in
> addition less robust.
>
> That being said, the crashing code in particular makes me wonder:
>
> static __always_inline void add_page_to_lru_list(struct page *page,
> struct lruvec *lruvec, enum lru_list lru)
> {
> int nr_pages = hpage_nr_pages(page);
> mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
> list_add(&page->lru, &lruvec->lists[lru]);
> __mod_zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru, nr_pages);
> }
>
> Why did we ever pass zone in here and then felt the need to replace it
> with lruvec->zone in fa9add6 "mm/memcg: apply add/del_page to lruvec"?
> A page does not roam between zones, its zone is a static property that
> can be retrieved with page_zone().
Hmm, if we don't update lruvec_zone(lruvec) when a node is onlined,
lruver_zone(lruvec) contains a invalid pointer, so we should check
all place that accesses lruvec_zone(lruvec). We store zone in lruvec
but we can't access it. And we can't avoid to access it in the
furture. So I think it is better to update it when the node is
onlined.
Thanks
Wen Congyang
>
> Johannes
>
>> [ 63.413436] BUG: unable to handle kernel NULL pointer dereference at 0000000000000f60
>> [ 63.414161] IP: [<ffffffff811870b9>] __mod_zone_page_state+0x9/0x60
>> [ 63.414161] PGD 0
>> [ 63.414161] Oops: 0000 [#1] SMP
>> [ 63.414161] Modules linked in: acpi_memhotplug binfmt_misc dm_mirror dm_region_hash dm_log dm_mod ppdev sg microcode pcspkr virtio_console virtio_balloon snd_intel8x0 snd_ac9
>> 7_codec ac97_bus snd_seq snd_seq_device snd_pcm snd_timer snd soundcore snd_page_alloc e1000 i2c_piix4 i2c_core floppy parport_pc parport sr_mod cdrom virtio_blk pata_acpi ata_g
>> eneric ata_piix libata scsi_mod
>> [ 63.414161] CPU 2
>> [ 63.414161] Pid: 1219, comm: numactl Not tainted 3.6.0-rc5+ #180 Bochs Bochs
>> ...
>> [ 63.414161] Process numactl (pid: 1219, threadinfo ffff880039abc000, task ffff8800383c4ce0)
>> [ 63.414161] Stack:
>> [ 63.414161] ffff880039abdaf8 ffffffff8117390f ffff880039abdaf8 000000008167c601
>> [ 63.414161] ffffffff81174162 ffff88003a480f00 0000000000000001 ffff8800395e0000
>> [ 63.414161] ffff88003dbd0e80 0000000000000282 ffff880039abdb48 ffffffff81174181
>> [ 63.414161] Call Trace:
>> [ 63.414161] [<ffffffff8117390f>] __pagevec_lru_add_fn+0xdf/0x140
>> [ 63.414161] [<ffffffff81174162>] ? pagevec_lru_move_fn+0x92/0x100
>> [ 63.414161] [<ffffffff81174181>] pagevec_lru_move_fn+0xb1/0x100
>> [ 63.414161] [<ffffffff81173830>] ? lru_add_page_tail+0x1b0/0x1b0
>> [ 63.414161] [<ffffffff811dff71>] ? exec_mmap+0x121/0x230
>> [ 63.414161] [<ffffffff811741ec>] __pagevec_lru_add+0x1c/0x30
>> [ 63.414161] [<ffffffff81174383>] lru_add_drain_cpu+0xa3/0x130
>> [ 63.414161] [<ffffffff8117443f>] lru_add_drain+0x2f/0x40
>> [ 63.414161] [<ffffffff81196da9>] exit_mmap+0x69/0x160
>> [ 63.414161] [<ffffffff810db115>] ? lock_release_holdtime+0x35/0x1a0
>> [ 63.414161] [<ffffffff81069c37>] mmput+0x77/0x100
>> [ 63.414161] [<ffffffff811dffc0>] exec_mmap+0x170/0x230
>> [ 63.414161] [<ffffffff811e0152>] flush_old_exec+0xd2/0x140
>> [ 63.414161] [<ffffffff812343ea>] load_elf_binary+0x32a/0xe70
>> [ 63.414161] [<ffffffff810d700d>] ? trace_hardirqs_off+0xd/0x10
>> [ 63.414161] [<ffffffff810b231f>] ? local_clock+0x6f/0x80
>> [ 63.414161] [<ffffffff810db115>] ? lock_release_holdtime+0x35/0x1a0
>> [ 63.414161] [<ffffffff810dd813>] ? __lock_release+0x133/0x1a0
>> [ 63.414161] [<ffffffff811e22e7>] ? search_binary_handler+0x1a7/0x4a0
>> [ 63.414161] [<ffffffff811e22f3>] search_binary_handler+0x1b3/0x4a0
>> [ 63.414161] [<ffffffff811e2194>] ? search_binary_handler+0x54/0x4a0
>> [ 63.414161] [<ffffffff812340c0>] ? set_brk+0xe0/0xe0
>> [ 63.414161] [<ffffffff811e284f>] do_execve_common+0x26f/0x320
>> [ 63.414161] [<ffffffff811bde33>] ? kmem_cache_alloc+0x113/0x220
>> [ 63.414161] [<ffffffff811e298a>] do_execve+0x3a/0x40
>> [ 63.414161] [<ffffffff8102061a>] sys_execve+0x4a/0x80
>> [ 63.414161] [<ffffffff81686c6c>] stub_execve+0x6c/0xc0
>> [ 63.414161] Code: ff 03 00 00 48 c1 e7 0b 48 c1 e2 07 48 29 d7 48 03 3c c5 c0 27 d2 81 e8 a6 fe ff ff c9 c3 0f 1f 40 00 55 48 89 e5 0f 1f 44 00 00 <48> 8b 4f 60 89 f6 48 8d 44 31 40 65 44 8a 40 02 45 0f be c0 41
>>
>> The reason is that we don't update root_mem_cgroup->info.nodeinfo[nid]->zoneinfo[zone].lruvec.zone
>> when onlining the node, and we try to access it.
>>
>> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
>> Reported-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>
>> ---
>> include/linux/memcontrol.h | 7 +++++++
>> mm/memcontrol.c | 14 ++++++++++++++
>> mm/memory_hotplug.c | 2 ++
>> 3 files changed, 23 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 8d9489f..87d8b77 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -182,6 +182,9 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>> unsigned long *total_scanned);
>>
>> void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
>> +
>> +void update_root_mem_cgroup(int nid);
>> +
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> void mem_cgroup_split_huge_fixup(struct page *head);
>> #endif
>> @@ -374,6 +377,10 @@ static inline void mem_cgroup_replace_page_cache(struct page *oldpage,
>> struct page *newpage)
>> {
>> }
>> +
>> +static inline void update_root_mem_cgroup(int nid)
>> +{
>> +}
>> #endif /* CONFIG_MEMCG */
>>
>> #if !defined(CONFIG_MEMCG) || !defined(CONFIG_DEBUG_VM)
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 795e525..c997a46 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -3427,6 +3427,20 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
>> __mem_cgroup_commit_charge(memcg, newpage, 1, type, true);
>> }
>>
>> +/* NODE_DATA(nid) is changed */
>> +void update_root_mem_cgroup(int nid)
>> +{
>> + struct mem_cgroup_per_node *pn;
>> + struct mem_cgroup_per_zone *mz;
>> + int zone;
>> +
>> + pn = root_mem_cgroup->info.nodeinfo[nid];
>> + for (zone = 0; zone < MAX_NR_ZONES; zone++) {
>> + mz = &pn->zoneinfo[zone];
>> + lruvec_init(&mz->lruvec, &NODE_DATA(nid)->node_zones[zone]);
>> + }
>> +}
>> +
>> #ifdef CONFIG_DEBUG_VM
>> static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
>> {
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 3ad25f9..bf03b02 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -555,6 +555,8 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>>
>> /* we can use NODE_DATA(nid) from here */
>>
>> + update_root_mem_cgroup(nid);
>> +
>> /* init node's zones as empty zones, we don't have any present pages.*/
>> free_area_init_node(nid, zones_size, start_pfn, zholes_size);
>>
>> --
>> 1.7.1
>
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