Re: [PATCH 3/3] mm/memory-failure: send SIGBUS in the event of thp split fail

Miaohe Lin
2024-05-05T07:00:30Z

On 2024/5/2 7:24, Jane Chu wrote:
> When handle hwpoison in a GUP longterm pin'ed thp page,
> try_to_split_thp_page() will fail. And at this point, there is little else
> the kernel could do except sending a SIGBUS to the user process, thus
> give it a chance to recover.
>
> Signed-off-by: Jane Chu <jane.chu@oracle.com>

Thanks for your patch. Some comments below.

> ---
> mm/memory-failure.c | 36 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 7fcf182abb96..67f4d24a98e7 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2168,6 +2168,37 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> return rc;
> }
>
> +/*
> + * The calling condition is as such: thp split failed, page might have
> + * been GUP longterm pinned, not much can be done for recovery.
> + * But a SIGBUS should be delivered with vaddr provided so that the user
> + * application has a chance to recover. Also, application processes'
> + * election for MCE early killed will be honored.
> + */
> +static int kill_procs_now(struct page *p, unsigned long pfn, int flags,
> + struct page *hpage)
> +{
> + struct folio *folio = page_folio(hpage);
> + LIST_HEAD(tokill);
> + int res = -EHWPOISON;
> +
> + /* deal with user pages only */
> + if (PageReserved(p) || PageSlab(p) || PageTable(p) || PageOffline(p))
> + res = -EBUSY;
> + if (!(PageLRU(hpage) || PageHuge(p)))
> + res = -EBUSY;

Above checks seems unneeded. We already know it's thp?

> +
> + if (res == -EHWPOISON) {
> + collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
> + kill_procs(&tokill, true, pfn, flags);
> + }
> +
> + if (flags & MF_COUNT_INCREASED)
> + put_page(p);

This if block is broken. put_page() has been done when try_to_split_thp_page() fails?

> +

action_result is missing?

> + return res;
> +}
> +
> /**
> * memory_failure - Handle memory failure of a page.
> * @pfn: Page Number of the corrupted page
> @@ -2297,6 +2328,11 @@ int memory_failure(unsigned long pfn, int flags)
> */
> SetPageHasHWPoisoned(hpage);
> if (try_to_split_thp_page(p) < 0) {

Should hwpoison_filter() be called in this case?

> + if (flags & MF_ACTION_REQUIRED) {
> + pr_err("%#lx: thp split failed\n", pfn);
> + res = kill_procs_now(p, pfn, flags, hpage);

Can we use hwpoison_user_mappings() directly here?

Thanks.
.

> + goto unlock_mutex;
> + }
> res = action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
> goto unlock_mutex;
> }
>