Messages in this thread | | | Date | Mon, 6 May 2024 13:26:19 -0700 | Subject | Re: [PATCH 3/3] mm/memory-failure: send SIGBUS in the event of thp split fail | From | Jane Chu <> |
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On 5/5/2024 12:00 AM, Miaohe Lin wrote:
> 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?
Agreed.
I lifted these checks from hwpoison_user_mapping() with a hope to make kill_procs_now() more generic,
such as, potentially replacing kill_accessing_processes() for re-accessing hwpoisoned page.
But I backed out at last, due to concerns that my tests might not have covered sufficient number of scenarios.
> >> + >> + 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?
put_page() has not been done if try_to_split_thp_page() fails, and I think it should.
I will revise the code so that put_page() is called regardless MF_ACTION_REQUIRED is set or not.
> >> + > action_result is missing?
Indeed, action_result() isn't always called, referring to the re-accessing hwpoison scenarios.
In this case, I think the reason is that, we just killed the process and there is nothing
else to do or to report.
> >> + 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? Yes, it should. I will add the hwpoison_filter check. > >> + 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?
I thought about using hwpoison_user_mappings() with an extra flag, but gave up in the end.
Because most of the code there are not needed, such as the checks you mentioned above,
and umapping etc.
thanks!
-jane
> > Thanks. > . > >> + goto unlock_mutex; >> + } >> res = action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED); >> goto unlock_mutex; >> } >>
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