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dkim=pass header.d=oracle.com header.s=corp-2021-07-09 header.b=1CFRE++t; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=dcZH9rvS; dmarc=pass (policy=none) header.from=oracle.com; spf=none (imf17.hostedemail.com: domain of mike.kravetz@oracle.com has no SPF policy when checking 205.220.165.32) smtp.mailfrom=mike.kravetz@oracle.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: CE585400AE X-Rspam-User: X-Stat-Signature: qwpuxb51f8zjgsy1szpczmnnq6bu7kyi X-HE-Tag: 1652324804-381176 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 5/11/22 19:54, Miaohe Lin wrote: > On 2022/5/12 2:35, Mike Kravetz wrote: >> On 5/11/22 08:19, Naoya Horiguchi wrote: >>> From: Naoya Horiguchi >>> >>> If memory_failure() fails to grab page refcount on a hugetlb page >>> because it's busy, it returns without setting PG_hwpoison on it. >>> This not only loses a chance of error containment, but breaks the rule >>> that action_result() should be called only when memory_failure() do >>> any of handling work (even if that's just setting PG_hwpoison). >>> This inconsistency could harm code maintainability. >>> >>> So set PG_hwpoison and call hugetlb_set_page_hwpoison() for such a case. > > I'm sorry but where is hugetlb_set_page_hwpoison() defined and used ? I can't find it. > >>> >>> Fixes: 405ce051236c ("mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()") >>> Signed-off-by: Naoya Horiguchi >>> --- >>> include/linux/mm.h | 1 + >>> mm/memory-failure.c | 8 ++++---- >>> 2 files changed, 5 insertions(+), 4 deletions(-) >>> >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index d446e834a3e5..04de0c3e4f9f 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -3187,6 +3187,7 @@ enum mf_flags { >>> MF_MUST_KILL = 1 << 2, >>> MF_SOFT_OFFLINE = 1 << 3, >>> MF_UNPOISON = 1 << 4, >>> + MF_NO_RETRY = 1 << 5, >>> }; >>> extern int memory_failure(unsigned long pfn, int flags); >>> extern void memory_failure_queue(unsigned long pfn, int flags); >>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>> index 6a28d020a4da..e3269b991016 100644 >>> --- a/mm/memory-failure.c >>> +++ b/mm/memory-failure.c >>> @@ -1526,7 +1526,8 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags) >>> count_increased = true; >>> } else { >>> ret = -EBUSY; >>> - goto out; >>> + if (!(flags & MF_NO_RETRY)) >>> + goto out; >>> } >> >> Hi Naoya, >> >> We are in the else block because !HPageFreed() and !HPageMigratable(). >> IIUC, this likely means the page is isolated. One common reason for isolation >> is migration. So, the page could be isolated and on a list for migration. >> >> I took a quick look at the hugetlb migration code and did not see any checks >> for PageHWPoison after a hugetlb page is isolated. I could have missed >> something? If there are no checks, we will read the PageHWPoison page >> in kernel mode while copying to the migration target. >> >> Is this an issue? Is is something we need to be concerned with? Memory >> errors can happen at any time, and gracefully handling them is best effort. > > It seems HWPoison hugetlb page will still be accessed before this patch. Can we do a > get_page_unless_zero first here to ensure that hugetlb page migration should fail due > to this extra page reference and thus not access the page content? If hugetlb page is > already freezed, corrupted memory will still be consumed though. :( Right. This potential issue was not introduced with this patch. Also, I am not sure but it might be an issue with non-hugetlb pages as well. As mentioned, memory error handling is a best effort. Since errors can happen at any time, we can not handle all cases. Or, you could spend the rest of your life trying. :) The question is, should we worry about errors that happen when a page is isolated for migration? -- Mike Kravetz