Messages in this thread | | | Date | Thu, 9 May 2024 08:34:37 -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 5/9/2024 1:30 AM, Miaohe Lin wrote: > On 2024/5/9 1:45, Jane Chu wrote: >> 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() ? > If you want to send SIGBUS in the event of thp split fail, it might be required to do so. > I think kill_procs_now() needs extra thp refcnt to do its work.
Agreed. I added an boolean to try_to_split_thp_page(),the boolean indicates whether to put_page().
In case of kill_procs_now(), put_page() is called afterwards.
> >>>> 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) { > I tend to agree MCE-early-kill request should be honored when try to kill process. > Thanks. > .
Thanks,
-jane
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