Re: [PATCH V2] mm/memory-failure: Ensure collect_procs is retried when unmap fails

[Jiaqi Yan <jiaqiyan@google.com>]

On Tue, Sep 23, 2025 at 7:57 AM shengminghu512 <shengminghu512@qq.com> wrote:
>
> From: Shengming Hu <shengminghu512@qq.com>
> Date: Tue, 23 Sep 2025 20:56:28 +0800
> Subject: [PATCH V2] mm/memory-failure: Ensure collect_procs is retried when
>  unmap fails
>
> In the memory_failure process, if collect_procs is not executed with the
> flag set, the to_kill list may be empty. Even if there are pages that fail

Hi Shengming,

I am trying to figure out what your code is for.

If we get into hwpoison_user_mappings with MF_ACTION_REQUIRED *not*
set in flags, force_early should not be set and it is totally valid
that collect_procs add nothing to to kill...

> to be unmapped, SIGKILL or SIGBUS cannot be sent to the process via

unless some process opt-ed in MCE_KILL_EARLY and collect_procs will
find that process if it mapped the poisoned page, regardless if
force_early is 1 or 0.

IOW I don't think there is any reason (no bug to fix and nothing to
improve) for what you are trying to do here.

> collect_procs.
>
> This patch fixes the issue by re-executing collect_procs when the to_kill
> list is empty and unmap fails. This collects processes with unmap failures
> into the to_kill list, allowing SIGBUS or SIGKILL to terminate them in
> subsequent code.
>
> V2:
>   - Resent as plain text (previous version was HTML).
>   - No functional changes.
>
> Signed-off-by: Shengming Hu <hu.shengming@zte.com.cn>
> ---
>  mm/memory-failure.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index a24806bb8e82..8157823c7fb7 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1600,9 +1600,12 @@ static bool hwpoison_user_mappings(struct folio *folio, struct page *p,
>         collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
>
>         unmap_success = !unmap_poisoned_folio(folio, pfn, flags & MF_MUST_KILL);
> -       if (!unmap_success)
> +       if (!unmap_success) {
>                 pr_err("%#lx: failed to unmap page (folio mapcount=%d)\n",
>                        pfn, folio_mapcount(folio));
> +               if (list_empty(&tokill))
> +                       collect_procs(folio, p, &tokill, 1);
> +       }
>
>         /*
>          * try_to_unmap() might put mlocked page in lru cache, so call
> --
> 2.25.1