Re: [syzbot] WARNING in folio_lruvec_lock_irqsave

[Muchun Song <songmuchun@bytedance.com>]

On Wed, Jun 22, 2022 at 06:49:31AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    ac0ba5454ca8 Add linux-next specific files for 20220622
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14354c18080000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=12809dacb9e7c5e0
> dashboard link: https://syzkaller.appspot.com/bug?extid=ec972d37869318fc3ffb
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ec972d37869318fc3ffb@syzkaller.appspotmail.com
> 
>  folio_put include/linux/mm.h:1227 [inline]
>  put_page+0x217/0x280 include/linux/mm.h:1279
>  unmap_and_move_huge_page mm/migrate.c:1343 [inline]
>  migrate_pages+0x3dc3/0x5a10 mm/migrate.c:1440
>  do_mbind mm/mempolicy.c:1332 [inline]
>  kernel_mbind+0x4d7/0x7d0 mm/mempolicy.c:1479
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> page has been migrated, last migrate reason: mempolicy_mbind
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 18925 at include/linux/memcontrol.h:800 folio_lruvec include/linux/memcontrol.h:800 [inline]

The warning here is "VM_WARN_ON_ONCE_FOLIO(!memcg && !mem_cgroup_disabled(), folio)",
the memcg returned by folio_memcg() seems to be NULL which has 2 possibility, one is
that objcg returned by folio_objcg() is NULL, another is that obj_cgroup_memcg(objcg)
returns NULL. However, obj_cgroup_memcg() always returns a valid memcg. So Most likely
objcg is NULL meaning this page is not charged to memcg. Is this possible for LRU pages?

I am not sure if this issue is caused by my commit cca700a8e695 ("mm: lru: use lruvec
lock to serialize memcg changes") since I have removed folio_test_clear_lru() check
from folio_batch_move_lru(). We know that a non-lru page may be not charged to memcg.
But is it possible for a non-lru page to be passed to folio_batch_move_lru()? Seems
impossible. Right? I am not very confident about this commit, hopefully, someone can
review it.

Thanks.

> WARNING: CPU: 1 PID: 18925 at include/linux/memcontrol.h:800 folio_lruvec_lock_irqsave+0x2fd/0x4f0 mm/memcontrol.c:1424
> Modules linked in:
> CPU: 1 PID: 18925 Comm: syz-executor.3 Not tainted 5.19.0-rc3-next-20220622-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:folio_lruvec include/linux/memcontrol.h:800 [inline]
> RIP: 0010:folio_lruvec_lock_irqsave+0x2fd/0x4f0 mm/memcontrol.c:1424
> Code: 1f 44 00 00 45 31 e4 80 3d 06 3e da 0b 00 0f 85 01 fe ff ff 48 c7 c6 40 6f da 89 4c 89 f7 e8 0a 44 e2 ff c6 05 ea 3d da 0b 01 <0f> 0b e9 e4 fd ff ff e8 67 be ad 07 85 c0 0f 84 37 fd ff ff 80 3d
> RSP: 0018:ffffc9000b84f2c8 EFLAGS: 00010246
> RAX: 0000000000040000 RBX: fffff9400027e007 RCX: ffffc900135af000
> RDX: 0000000000040000 RSI: ffffffff81ce36a6 RDI: fffff52001709e28
> RBP: dffffc0000000000 R08: 000000000000003c R09: 0000000000000000
> R10: 0000000080000001 R11: 0000000000000001 R12: 0000000000000000
> R13: fffff9400027e000 R14: ffffea00013f0000 R15: 0000000000000000
> FS:  00007f5cfbb96700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000002073f000 CR3: 0000000074b9f000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  folio_lruvec_relock_irqsave include/linux/memcontrol.h:1666 [inline]
>  folio_batch_move_lru+0xf9/0x500 mm/swap.c:242
>  folio_batch_add_and_move+0xd4/0x130 mm/swap.c:258
>  deactivate_file_folio+0x222/0x580 mm/swap.c:678
>  invalidate_mapping_pagevec+0x38d/0x5c0 mm/truncate.c:535
>  drop_pagecache_sb+0xcf/0x2a0 fs/drop_caches.c:39
>  iterate_supers+0x13c/0x290 fs/super.c:694
>  drop_caches_sysctl_handler+0xdb/0x110 fs/drop_caches.c:62
>  proc_sys_call_handler+0x4a1/0x6e0 fs/proc/proc_sysctl.c:611
>  call_write_iter include/linux/fs.h:2057 [inline]
>  do_iter_readv_writev+0x3d1/0x640 fs/read_write.c:742
>  do_iter_write+0x182/0x700 fs/read_write.c:868
>  vfs_iter_write+0x70/0xa0 fs/read_write.c:909
>  iter_file_splice_write+0x723/0xc70 fs/splice.c:689
>  do_splice_from fs/splice.c:767 [inline]
>  direct_splice_actor+0x110/0x180 fs/splice.c:936
>  splice_direct_to_actor+0x34b/0x8c0 fs/splice.c:891
>  do_splice_direct+0x1a7/0x270 fs/splice.c:979
>  do_sendfile+0xae0/0x1240 fs/read_write.c:1262
>  __do_sys_sendfile64 fs/read_write.c:1321 [inline]
>  __se_sys_sendfile64 fs/read_write.c:1313 [inline]
>  __x64_sys_sendfile64+0x149/0x210 fs/read_write.c:1313
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> RIP: 0033:0x7f5cfaa89109
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f5cfbb96168 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
> RAX: ffffffffffffffda RBX: 00007f5cfab9c030 RCX: 00007f5cfaa89109
> RDX: 0000000020002080 RSI: 0000000000000005 RDI: 0000000000000006
> RBP: 00007f5cfaae305d R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000262 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fff1ef394df R14: 00007f5cfbb96300 R15: 0000000000022000
>  </TASK>
> 
> 
> ---
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