Re: [PATCH v2] mm/memory-failure.c: skip huge_zero_page in memory_failure()

[Yang Shi <shy828301@gmail.com>]

On Thu, Apr 21, 2022 at 2:03 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 21.04.22 01:38, Yang Shi wrote:
> > On Tue, Apr 12, 2022 at 8:11 AM Xu Yu <xuyu@linux.alibaba.com> wrote:
> >>
> >> Kernel panic when injecting memory_failure for the global huge_zero_page,
> >> when CONFIG_DEBUG_VM is enabled, as follows.
> >>
> >> [    5.582720] Injecting memory failure for pfn 0x109ff9 at process virtual address 0x20ff9000
> >> [    5.583786] page:00000000fb053fc3 refcount:2 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x109e00
> >> [    5.584900] head:00000000fb053fc3 order:9 compound_mapcount:0 compound_pincount:0
> >> [    5.585796] flags: 0x17fffc000010001(locked|head|node=0|zone=2|lastcpupid=0x1ffff)
> >> [    5.586712] raw: 017fffc000010001 0000000000000000 dead000000000122 0000000000000000
> >> [    5.587640] raw: 0000000000000000 0000000000000000 00000002ffffffff 0000000000000000
> >> [    5.588565] page dumped because: VM_BUG_ON_PAGE(is_huge_zero_page(head))
> >> [    5.589398] ------------[ cut here ]------------
> >> [    5.589952] kernel BUG at mm/huge_memory.c:2499!
> >> [    5.590516] invalid opcode: 0000 [#1] PREEMPT SMP PTI
> >> [    5.591120] CPU: 6 PID: 553 Comm: split_bug Not tainted 5.18.0-rc1+ #11
> >> [    5.591904] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 3288b3c 04/01/2014
> >> [    5.592817] RIP: 0010:split_huge_page_to_list+0x66a/0x880
> >> [    5.593469] Code: 84 9b fb ff ff 48 8b 7c 24 08 31 f6 e8 9f 5d 2a 00 b8 b8 02 00 00 e9 e8 fb ff ff 48 c7 c6 e8 47 3c 82 4c b
> >> [    5.595806] RSP: 0018:ffffc90000dcbdf8 EFLAGS: 00010246
> >> [    5.596434] RAX: 000000000000003c RBX: 0000000000000001 RCX: 0000000000000000
> >> [    5.597322] RDX: 0000000000000000 RSI: ffffffff823e4c4f RDI: 00000000ffffffff
> >> [    5.598162] RBP: ffff88843fffdb40 R08: 0000000000000000 R09: 00000000fffeffff
> >> [    5.598999] R10: ffffc90000dcbc48 R11: ffffffff82d68448 R12: ffffea0004278000
> >> [    5.599849] R13: ffffffff823c6203 R14: 0000000000109ff9 R15: ffffea000427fe40
> >> [    5.600693] FS:  00007fc375a26740(0000) GS:ffff88842fd80000(0000) knlGS:0000000000000000
> >> [    5.601640] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [    5.602304] CR2: 00007fc3757c9290 CR3: 0000000102174006 CR4: 00000000003706e0
> >> [    5.603139] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> [    5.603977] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> [    5.604806] Call Trace:
> >> [    5.605101]  <TASK>
> >> [    5.605357]  ? __irq_work_queue_local+0x39/0x70
> >> [    5.605904]  try_to_split_thp_page+0x3a/0x130
> >> [    5.606430]  memory_failure+0x128/0x800
> >> [    5.606888]  madvise_inject_error.cold+0x8b/0xa1
> >> [    5.607444]  __x64_sys_madvise+0x54/0x60
> >> [    5.607915]  do_syscall_64+0x35/0x80
> >> [    5.608347]  entry_SYSCALL_64_after_hwframe+0x44/0xae
> >> [    5.608949] RIP: 0033:0x7fc3754f8bf9
> >> [    5.609374] Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 8
> >> [    5.611554] RSP: 002b:00007ffeda93a1d8 EFLAGS: 00000217 ORIG_RAX: 000000000000001c
> >> [    5.612441] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc3754f8bf9
> >> [    5.613269] RDX: 0000000000000064 RSI: 0000000000003000 RDI: 0000000020ff9000
> >> [    5.614108] RBP: 00007ffeda93a200 R08: 0000000000000000 R09: 0000000000000000
> >> [    5.614946] R10: 00000000ffffffff R11: 0000000000000217 R12: 0000000000400490
> >> [    5.615787] R13: 00007ffeda93a2e0 R14: 0000000000000000 R15: 0000000000000000
> >> [    5.616626]  </TASK>
> >>
> >> This makes huge_zero_page bail out explicitly before split in
> >> memory_failure(), thus the panic above won't happen again.
> >
> > Skipping huge_zero_page in error injection is ok to me, but I'm
> > actually wondering whether raising BUG is overkilling for splitting
> > huge_zero_page or not. Returning -EBUSY should be totally fine.
>
> I tend to agree. Just failing with -EBUSY might be cleaner. Most
> probably we want to catch any bogus code here that does something we
> don't really expect -- splitting the huge zeropage makes 0 sense.

Yeah, the huge zero page can't be met from normal paths other than
memory failure, but memory failure is a valid caller. So I tend to
replace the BUG to WARN + returning -EBUSY. If we don't care about the
reason code in memory failure, we don't have to touch memory failure.

>
> --
> Thanks,
>
> David / dhildenb
>
>