Messages in this thread | | | Date | Wed, 8 May 2024 10:45:15 -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 5/8/2024 1:08 AM, Miaohe Lin wrote:
> On 2024/5/7 4:26, Jane Chu wrote: >> 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. > In try_to_split_thp_page(), if split_huge_page fails, i.e. ret != 0, put_page() is called. See below: > > static int try_to_split_thp_page(struct page *page) > { > int ret; > > lock_page(page); > ret = split_huge_page(page); > unlock_page(page); > > if (unlikely(ret)) > put_page(page); > ^^^^^^^^^^^^^^^^^^^^^^^ > return ret; > } > > Or am I miss something?
I think you caught a bug in my code, thanks!
How about moving put_page() outside try_to_split_thp_page() ?
> >> 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) { > Only in MF_ACTION_REQUIRED case, SIGBUS is sent to processes when thp split failed. Any reson under it?
I took a clue from kill_accessing_process() which is invoked only if MF_ACTION_REQUIRED is set.
The usual code path for delivery signal is
if page-is-dirty or MF_MUST_KILL-is-set or umap-failed, then
- send SIGKILL if vaddr is -EFAULT
- send SIGBUS with BUS_MCEERR_AR if MF_ACTION_REQUIRED is set
- send SIGBUS with BUS_MCEERR_AO if MF_ACTION_REQUIRED is not set and process elected for MCE-early-kill
So, if kill_procs_now() is invoked only if MF_ACTION_REQUIRED (as it is in the patch), one can argue that
the MCE-early-kill request is not honored which deviates from the existing behavior.
Perhaps I should remove the
+ if (flags & MF_ACTION_REQUIRED) {
check.
thanks!
-jane
> > Thanks. > .
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