Messages in this thread | | | Date | Thu, 9 May 2024 20:18:46 -0700 | Subject | Re: [PATCH 3/3] mm/memory-failure: send SIGBUS in the event of thp split fail | From | Jane Chu <> |
| |
On 5/9/2024 7:59 PM, Miaohe Lin wrote: > On 2024/5/9 23:34, Jane Chu wrote: >> 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(). > IMHO, it might be too complicated to add an extra boolean to indicate whether to put_page(). It might be > more straightforward to always put_page outside try_to_split_thp_page?
Looks okay to me, let's see. Will send out v2 in a while.
thanks,
-jane
> Thanks. > . >
| |