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SubjectRe: list corruption in deferred_split_scan()
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On 7/13/19 8:53 PM, Hillf Danton wrote:
> On Wed, 10 Jul 2019 14:43:28 -0700 (PDT) Qian Cai wrote:
>> Running LTP oom01 test case with swap triggers a crash below. Revert the series
>> "Make deferred split shrinker memcg aware" [1] seems fix the issue.
>>
>> aefde94195ca mm: thp: make deferred split shrinker memcg aware
>> cf402211cacc mm-shrinker-make-shrinker-not-depend-on-memcg-kmem-fix-2-fix
>> ca37e9e5f18d mm-shrinker-make-shrinker-not-depend-on-memcg-kmem-fix-2
>> 5f419d89cab4 mm-shrinker-make-shrinker-not-depend-on-memcg-kmem-fix
>> c9d49e69e887 mm: shrinker: make shrinker not depend on memcg kmem
>> 1c0af4b86bcf mm: move mem_cgroup_uncharge out of __page_cache_release()
>> 4e050f2df876 mm: thp: extract split_queue_* into a struct
>>
>> [1] https://lore.kernel.org/linux-mm/1561507361-59349-1-git-send-email-yang.shi@linux.alibaba.com/
>>
>> [ 1145.730682][ T5764] list_del corruption, ffffea00251c8098->next is LIST_POISON1 (dead000000000100)
>> [ 1145.739763][ T5764] ------------[ cut here ]------------
>> [ 1145.745126][ T5764] kernel BUG at lib/list_debug.c:47!
>> [ 1145.750320][ T5764] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
>> [ 1145.757513][ T5764] CPU: 1 PID: 5764 Comm: oom01 Tainted: G        W         5.2.0-next-20190710+ #7
>> [ 1145.766709][ T5764] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 01/25/2019
>> [ 1145.776000][ T5764] RIP: 0010:__list_del_entry_valid.cold.0+0x12/0x4a
>> [ 1145.782491][ T5764] Code: c7 40 5a 33 af e8 ac fe bc ff 0f 0b 48 c7 c7 80 9e
>> a1 af e8 f6 4c 01 00 4c 89 ea 48 89 de 48 c7 c7 20 59 33 af e8 8c fe bc ff <0f>
>> 0b 48 c7 c7 40 9f a1 af e8 d6 4c 01 00 4c 89 e2 48 89 de 48 c7
>> [ 1145.802078][ T5764] RSP: 0018:ffff888514d773c0 EFLAGS: 00010082
>> [ 1145.808042][ T5764] RAX: 000000000000004e RBX: ffffea00251c8098 RCX: ffffffffae95d318
>> [ 1145.815923][ T5764] RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff8888440bd380
>> [ 1145.823806][ T5764] RBP: ffff888514d773d8 R08: ffffed1108817a71 R09: ffffed1108817a70
>> [ 1145.831689][ T5764] R10: ffffed1108817a70 R11: ffff8888440bd387 R12: dead000000000122
>> [ 1145.839571][ T5764] R13: dead000000000100 R14: ffffea00251c8034 R15: dead000000000100
>> [ 1145.847455][ T5764] FS:  00007f765ad4d700(0000) GS:ffff888844080000(0000) knlGS:0000000000000000
>> [ 1145.856299][ T5764] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 1145.862784][ T5764] CR2: 00007f8cebec7000 CR3: 0000000459338000 CR4: 00000000001406a0
>> [ 1145.870664][ T5764] Call Trace:
>> [ 1145.873835][ T5764]  deferred_split_scan+0x337/0x740
>> [ 1145.878835][ T5764]  ? split_huge_page_to_list+0xe30/0xe30
>> [ 1145.884364][ T5764]  ? __radix_tree_lookup+0x12d/0x1e0
>> [ 1145.889539][ T5764]  ? node_tag_get.part.0.constprop.6+0x40/0x40
>> [ 1145.895592][ T5764]  do_shrink_slab+0x244/0x5a0
>> [ 1145.900159][ T5764]  shrink_slab+0x253/0x440
>> [ 1145.904462][ T5764]  ? unregister_shrinker+0x110/0x110
>> [ 1145.909641][ T5764]  ? kasan_check_read+0x11/0x20
>> [ 1145.914383][ T5764]  ? mem_cgroup_protected+0x20f/0x260
>> [ 1145.919645][ T5764]  shrink_node+0x31e/0xa30
>> [ 1145.923949][ T5764]  ? shrink_node_memcg+0x1560/0x1560
>> [ 1145.929126][ T5764]  ? ktime_get+0x93/0x110
>> [ 1145.933340][ T5764]  do_try_to_free_pages+0x22f/0x820
>> [ 1145.938429][ T5764]  ? shrink_node+0xa30/0xa30
>> [ 1145.942906][ T5764]  ? kasan_check_read+0x11/0x20
>> [ 1145.947647][ T5764]  ? check_chain_key+0x1df/0x2e0
>> [ 1145.952474][ T5764]  try_to_free_pages+0x242/0x4d0
>> [ 1145.957299][ T5764]  ? do_try_to_free_pages+0x820/0x820
>> [ 1145.962566][ T5764]  __alloc_pages_nodemask+0x9ce/0x1bc0
>> [ 1145.967917][ T5764]  ? kasan_check_read+0x11/0x20
>> [ 1145.972657][ T5764]  ? gfp_pfmemalloc_allowed+0xc0/0xc0
>> [ 1145.977920][ T5764]  ? kasan_check_read+0x11/0x20
>> [ 1145.982659][ T5764]  ? check_chain_key+0x1df/0x2e0
>> [ 1145.987487][ T5764]  ? do_anonymous_page+0x343/0xe30
>> [ 1145.992489][ T5764]  ? lock_downgrade+0x390/0x390
>> [ 1145.997230][ T5764]  ? __count_memcg_events+0x8b/0x1c0
>> [ 1146.002404][ T5764]  ? kasan_check_read+0x11/0x20
>> [ 1146.007145][ T5764]  ? __lru_cache_add+0x122/0x160
>> [ 1146.011974][ T5764]  alloc_pages_vma+0x89/0x2c0
>> [ 1146.016538][ T5764]  do_anonymous_page+0x3e1/0xe30
>> [ 1146.021367][ T5764]  ? __update_load_avg_cfs_rq+0x2c/0x490
>> [ 1146.026893][ T5764]  ? finish_fault+0x120/0x120
>> [ 1146.031461][ T5764]  ? call_function_interrupt+0xa/0x20
>> [ 1146.036724][ T5764]  handle_pte_fault+0x457/0x12c0
>> [ 1146.041552][ T5764]  __handle_mm_fault+0x79a/0xa50
>> [ 1146.046378][ T5764]  ? vmf_insert_mixed_mkwrite+0x20/0x20
>> [ 1146.051817][ T5764]  ? kasan_check_read+0x11/0x20
>> [ 1146.056557][ T5764]  ? __count_memcg_events+0x8b/0x1c0
>> [ 1146.061732][ T5764]  handle_mm_fault+0x17f/0x370
>> [ 1146.066386][ T5764]  __do_page_fault+0x25b/0x5d0
>> [ 1146.071037][ T5764]  do_page_fault+0x4c/0x2cf
>> [ 1146.075426][ T5764]  ? page_fault+0x5/0x20
>> [ 1146.079553][ T5764]  page_fault+0x1b/0x20
>> [ 1146.083594][ T5764] RIP: 0033:0x410be0
>> [ 1146.087373][ T5764] Code: 89 de e8 e3 23 ff ff 48 83 f8 ff 0f 84 86 00 00 00
>> 48 89 c5 41 83 fc 02 74 28 41 83 fc 03 74 62 e8 95 29 ff ff 31 d2 48 98 90 <c6>
>> 44 15 00 07 48 01 c2 48 39 d3 7f f3 31 c0 5b 5d 41 5c c3 0f 1f
>> [ 1146.106959][ T5764] RSP: 002b:00007f765ad4cec0 EFLAGS: 00010206
>> [ 1146.112921][ T5764] RAX: 0000000000001000 RBX: 00000000c0000000 RCX: 00007f98f2674497
>> [ 1146.120804][ T5764] RDX: 0000000001d95000 RSI: 00000000c0000000 RDI: 0000000000000000
>> [ 1146.128687][ T5764] RBP: 00007f74d9d4c000 R08: 00000000ffffffff R09: 0000000000000000
>> [ 1146.136569][ T5764] R10: 0000000000000022 R11: 000000000
>> [ 1147.588181][ T5764] Shutting down cpus with NMI
>> [ 1147.592756][ T5764] Kernel Offset: 0x2d400000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
>> [ 1147.604414][ T5764] ---[ end Kernel panic - not syncing: Fatal exception ]---
>
> Ignore the noise if there is no chance you think to corrupt the local list walk
> in some way like:
>
> CPU0 CPU1
> ---- ----
> take no lock spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> list_for_each_safe(pos, next,
> &list)
> list_del(page_deferred_list(page));
> page = list_entry((void *)pos,
> struct page, mapping);
> spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);

IMHO, I didn't see the race could happen really.

list_del() is called at 3 places:
1. Parallel free_transhuge_page(): The refcount bump should prevent from
the race.
2. Parallel reclaimer: split_queue_lock should prevent this, so the
other reclaimer should not see the same page.
3. Parallel split_huge_page(): I'm not sure about this one. But, page
lock should be acquired before calling split_huge_page() in other call
paths too.

I'm not sure if I miss anything, please feel free to correct me.

>
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2765,7 +2765,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
> if (!list_empty(page_deferred_list(head))) {
> ds_queue->split_queue_len--;
> - list_del(page_deferred_list(head));
> + list_del_init(page_deferred_list(head));
> }
> if (mapping)
> __dec_node_page_state(page, NR_SHMEM_THPS);
> @@ -2814,7 +2814,7 @@ void free_transhuge_page(struct page *page)
> spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> if (!list_empty(page_deferred_list(page))) {
> ds_queue->split_queue_len--;
> - list_del(page_deferred_list(page));
> + list_del_init(page_deferred_list(page));
> }
> spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
> free_compound_page(page);
> --

I proposed the similar thing.

> The major important is listed above; the minor trivial part below.
> Both are only for thought collectings.
>
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2869,9 +2869,8 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
> struct pglist_data *pgdata = NODE_DATA(sc->nid);
> struct deferred_split *ds_queue;
> unsigned long flags;
> - LIST_HEAD(list), *pos, *next;
> struct page *page;
> - int split = 0;
> + unsigned long nr_split = 0;
>
> #ifdef CONFIG_MEMCG
> if (sc->memcg)
> @@ -2884,44 +2883,44 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>
> spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> /* Take pin on all head pages to avoid freeing them under us */
> - list_for_each_safe(pos, next, &ds_queue->split_queue) {
> - page = list_entry((void *)pos, struct page, mapping);
> + while (sc->nr_to_scan && !list_empty(&ds_queue->split_queue)) {
> + bool locked, pinned;
> +
> + page = list_first_entry(&ds_queue->split_queue, struct page,
> + mapping);
> page = compound_head(page);
> +
> if (get_page_unless_zero(page)) {
> - list_move(page_deferred_list(page), &list);
> + pinned = true;
> + locked = trylock_page(page);
> } else {
> /* We lost race with put_compound_page() */
> - list_del_init(page_deferred_list(page));
> - ds_queue->split_queue_len--;
> + pinned = false;
> + locked = false;
> + }
> + list_del_init(page_deferred_list(page));
> + ds_queue->split_queue_len--;
> + --sc->nr_to_scan;
> + if (!pinned)
> + continue;
> + spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
> + if (locked) {
> + if (!split_huge_page(page))
> + nr_split++;
> + unlock_page(page);
> }
> - if (!--sc->nr_to_scan)
> - break;
> - }
> - spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
> -
> - list_for_each_safe(pos, next, &list) {
> - page = list_entry((void *)pos, struct page, mapping);
> - if (!trylock_page(page))
> - goto next;
> - /* split_huge_page() removes page from list on success */
> - if (!split_huge_page(page))
> - split++;
> - unlock_page(page);
> -next:
> put_page(page);
> + spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> }
> -
> - spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> - list_splice_tail(&list, &ds_queue->split_queue);
> spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>
> /*
> * Stop shrinker if we didn't split any page, but the queue is empty.
> * This can happen if pages were freed under us.
> */
> - if (!split && list_empty(&ds_queue->split_queue))
> + if (!nr_split && list_empty(&ds_queue->split_queue))
> return SHRINK_STOP;
> - return split;
> + return nr_split;
> }
>
> static struct shrinker deferred_split_shrinker = {
> --

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