Re: [PATCH 2/2 RESEND] mm/huge_memory: do not overkill when splitting huge_zero_page

[Yang Shi <shy828301@gmail.com>]

On Wed, Apr 27, 2022 at 2:45 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.
>
>   Injecting memory failure for pfn 0x109ff9 at process virtual address 0x20ff9000
>   page:00000000fb053fc3 refcount:2 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x109e00
>   head:00000000fb053fc3 order:9 compound_mapcount:0 compound_pincount:0
>   flags: 0x17fffc000010001(locked|head|node=0|zone=2|lastcpupid=0x1ffff)
>   raw: 017fffc000010001 0000000000000000 dead000000000122 0000000000000000
>   raw: 0000000000000000 0000000000000000 00000002ffffffff 0000000000000000
>   page dumped because: VM_BUG_ON_PAGE(is_huge_zero_page(head))
>   ------------[ cut here ]------------
>   kernel BUG at mm/huge_memory.c:2499!
>   invalid opcode: 0000 [#1] PREEMPT SMP PTI
>   CPU: 6 PID: 553 Comm: split_bug Not tainted 5.18.0-rc1+ #11
>   Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 3288b3c 04/01/2014
>   RIP: 0010:split_huge_page_to_list+0x66a/0x880
>   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
>   RSP: 0018:ffffc90000dcbdf8 EFLAGS: 00010246
>   RAX: 000000000000003c RBX: 0000000000000001 RCX: 0000000000000000
>   RDX: 0000000000000000 RSI: ffffffff823e4c4f RDI: 00000000ffffffff
>   RBP: ffff88843fffdb40 R08: 0000000000000000 R09: 00000000fffeffff
>   R10: ffffc90000dcbc48 R11: ffffffff82d68448 R12: ffffea0004278000
>   R13: ffffffff823c6203 R14: 0000000000109ff9 R15: ffffea000427fe40
>   FS:  00007fc375a26740(0000) GS:ffff88842fd80000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 00007fc3757c9290 CR3: 0000000102174006 CR4: 00000000003706e0
>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   Call Trace:
>   try_to_split_thp_page+0x3a/0x130
>   memory_failure+0x128/0x800
>   madvise_inject_error.cold+0x8b/0xa1
>   __x64_sys_madvise+0x54/0x60
>   do_syscall_64+0x35/0x80
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
>   RIP: 0033:0x7fc3754f8bf9
>   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
>   RSP: 002b:00007ffeda93a1d8 EFLAGS: 00000217 ORIG_RAX: 000000000000001c
>   RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc3754f8bf9
>   RDX: 0000000000000064 RSI: 0000000000003000 RDI: 0000000020ff9000
>   RBP: 00007ffeda93a200 R08: 0000000000000000 R09: 0000000000000000
>   R10: 00000000ffffffff R11: 0000000000000217 R12: 0000000000400490
>   R13: 00007ffeda93a2e0 R14: 0000000000000000 R15: 0000000000000000
>
> We think that raising BUG is overkilling for splitting huge_zero_page,
> the huge_zero_page can't be met from normal paths other than memory
> failure, but memory failure is a valid caller. So we tend to replace the
> BUG to WARN + returning -EBUSY, and thus the panic above won't happen
> again.

Reviewed-by: Yang Shi <shy828301@gmail.com>

>
> Suggested-by: Yang Shi <shy828301@gmail.com>
> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
> ---
>  mm/huge_memory.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c468fee595ff..910a138e9859 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2495,11 +2495,16 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>         struct address_space *mapping = NULL;
>         int extra_pins, ret;
>         pgoff_t end;
> +       bool is_hzp;
>
> -       VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
>         VM_BUG_ON_PAGE(!PageLocked(head), head);
>         VM_BUG_ON_PAGE(!PageCompound(head), head);
>
> +       is_hzp = is_huge_zero_page(head);
> +       VM_WARN_ON_ONCE_PAGE(is_hzp, head);
> +       if (is_hzp)
> +               return -EBUSY;
> +
>         if (PageWriteback(head))
>                 return -EBUSY;
>
> --
> 2.20.1.2432.ga663e714
>