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    SubjectRe: [PATCH v1 0/3] mm,hwpoison: fix sending SIGBUS for Action Required MCE
    On Tue, 13 Apr 2021 07:43:17 +0900
    Naoya Horiguchi <nao.horiguchi@gmail.com> wrote:

    > Hi,
    >
    > I wrote this patchset to materialize what I think is the current
    > allowable solution mentioned by the previous discussion [1].
    > I simply borrowed Tony's mutex patch and Aili's return code patch,
    > then I queued another one to find error virtual address in the best
    > effort manner. I know that this is not a perfect solution, but
    > should work for some typical case.
    >
    > My simple testing showed this patchset seems to work as intended,
    > but if you have the related testcases, could you please test and
    > let me have some feedback?
    >
    > Thanks,
    > Naoya Horiguchi
    >
    > [1]: https://lore.kernel.org/linux-mm/20210331192540.2141052f@alex-virtual-machine/
    > ---
    > Summary:
    >
    > Aili Yao (1):
    > mm,hwpoison: return -EHWPOISON when page already
    >
    > Naoya Horiguchi (1):
    > mm,hwpoison: add kill_accessing_process() to find error virtual address
    >
    > Tony Luck (1):
    > mm/memory-failure: Use a mutex to avoid memory_failure() races
    >
    > arch/x86/kernel/cpu/mce/core.c | 13 +++-
    > include/linux/swapops.h | 5 ++
    > mm/memory-failure.c | 166 ++++++++++++++++++++++++++++++++++++++++-
    > 3 files changed, 178 insertions(+), 6 deletions(-)

    Hi Naoya,

    Thanks for your patch and complete fix for this race issue.

    I test your patches, mainly it worked as expected, but in some cases it failed, I checked it
    and find some doubt places, could you help confirm it?

    1. there is a compile warning:
    static int hwpoison_pte_range(pmd_t *pmdp, unsigned long addr,
    unsigned long end, struct mm_walk *walk)
    {
    struct hwp_walk *hwp = (struct hwp_walk *)walk->private;
    int ret; ---- here

    It seems this ret may not be initialized, and some time ret may be error retruned?

    and for this:
    static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
    unsigned long poisoned_pfn, struct to_kill *tk)
    {
    unsigned long pfn;

    I think it better to be initialized too.

    2. In the function hwpoison_pte_range():
    if (pfn <= hwp->pfn && hwp->pfn < pfn + PMD_SIZE) this check seem we should use PMD_SIZE/PAGE_SIZE or some macro like this?

    3. unsigned long hwpoison_vaddr = addr + (hwp->pfn << PAGE_SHIFT & ~PMD_MASK); this seems not exact accurate?

    4. static int set_to_kill(struct to_kill *tk, unsigned long addr, short shift)
    {
    if (tk->addr) { --- I am not sure about this check and if it will lead failure.
    return 1;
    }
    In my test, it seems sometimes it will hit this branch, I don't know it's multi entry issue or multi posion issue.
    when i get to this fail, there is not enough log for this, but i can't reproduce it after that.

    wolud you help confirm this and if any changes, please post again and I will do the test again.

    Thansk
    Aili Yao

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