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This results in >> killing wrong processes. So set PageHWPoison flag with holding page lock, >> >> Signed-off-by: Naoya Horiguchi >> --- >> mm/memory-failure.c | 27 ++++++++++++--------------- >> 1 file changed, 12 insertions(+), 15 deletions(-) >> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> index ac6492e36978..fe25eee8f9d6 100644 >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -1494,24 +1494,11 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags) >> int res; >> unsigned long page_flags; >> >> - if (TestSetPageHWPoison(head)) { >> - pr_err("Memory failure: %#lx: already hardware poisoned\n", >> - pfn); >> - res = -EHWPOISON; >> - if (flags & MF_ACTION_REQUIRED) >> - res = kill_accessing_process(current, page_to_pfn(head), flags); >> - return res; >> - } >> - >> - num_poisoned_pages_inc(); >> - >> if (!(flags & MF_COUNT_INCREASED)) { >> res = get_hwpoison_page(p, flags); > > I'm not an expert of hugetlb, I may be wrong. I'm wondering how this > could solve the race? Is the below race still possible? > > __get_hwpoison_page() > head = compound_head(page) > > hugetlb demotion (1G --> 2M) > get_hwpoison_huge_page(head, &hugetlb); > > > Then the head may point to a 2M page, but the hwpoisoned subpage is > not in that 2M range? That is correct. It is also possible that __free_pages(page, huge_page_order(h)) could have been called during this window. So IIUC, head would have an increased ref count and pages would be freed to buddy when the memory error code drops the ref. At that time, head would be marked as poisoned which could be different than actual page with poison. An increased ref count, or page lock will not prevent hugetlb page demotion or (attempting) to free to buddy today. There is already a patch in Andrew's tree to not demote hugetlb pages marked with poison. This at least makes the demote code perform the same check as allocation code. The race which started this discussion has been there for a while. demotion opened another window, but that is now closed. IMO, it would be better to take a step back and look at the overall design and decide how to proceed. There is also an effort underway to provide double mapping of hugetlb pages, and one of the target use cases is memory error handling. This effort is in the very early stages, but it will certainly require setting poison on the (sub-)page with actual error rather than head page. Perhaps something like what is done for THP today. Nothing to address yet, but I just wanted to note there will be future changes in this area. -- Mike Kravetz