path: root/mm/memory-failure.c
diff options
authorNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>2018-08-23 17:00:38 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-08-23 18:48:43 -0700
commit6bc9b56433b76e40d11099338d27fbc5cd2935ca (patch)
tree3bfb85e2dc5f4a9367c720313c1ea9f4f4331c93 /mm/memory-failure.c
parentnamei: allow restricted O_CREAT of FIFOs and regular files (diff)
mm: fix race on soft-offlining free huge pages
Patch series "mm: soft-offline: fix race against page allocation". Xishi recently reported the issue about race on reusing the target pages of soft offlining. Discussion and analysis showed that we need make sure that setting PG_hwpoison should be done in the right place under zone->lock for soft offline. 1/2 handles free hugepage's case, and 2/2 hanldes free buddy page's case. This patch (of 2): There's a race condition between soft offline and hugetlb_fault which causes unexpected process killing and/or hugetlb allocation failure. The process killing is caused by the following flow: CPU 0 CPU 1 CPU 2 soft offline get_any_page // find the hugetlb is free mmap a hugetlb file page fault ... hugetlb_fault hugetlb_no_page alloc_huge_page // succeed soft_offline_free_page // set hwpoison flag mmap the hugetlb file page fault ... hugetlb_fault hugetlb_no_page find_lock_page return VM_FAULT_HWPOISON mm_fault_error do_sigbus // kill the process The hugetlb allocation failure comes from the following flow: CPU 0 CPU 1 mmap a hugetlb file // reserve all free page but don't fault-in soft offline get_any_page // find the hugetlb is free soft_offline_free_page // set hwpoison flag dissolve_free_huge_page // fail because all free hugepages are reserved page fault ... hugetlb_fault hugetlb_no_page alloc_huge_page ... dequeue_huge_page_node_exact // ignore hwpoisoned hugepage // and finally fail due to no-mem The root cause of this is that current soft-offline code is written based on an assumption that PageHWPoison flag should be set at first to avoid accessing the corrupted data. This makes sense for memory_failure() or hard offline, but does not for soft offline because soft offline is about corrected (not uncorrected) error and is safe from data lost. This patch changes soft offline semantics where it sets PageHWPoison flag only after containment of the error page completes successfully. Link: http://lkml.kernel.org/r/1531452366-11661-2-git-send-email-n-horiguchi@ah.jp.nec.com Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Reported-by: Xishi Qiu <xishi.qiuxishi@alibaba-inc.com> Suggested-by: Xishi Qiu <xishi.qiuxishi@alibaba-inc.com> Tested-by: Mike Kravetz <mike.kravetz@oracle.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: <zy.zhengyi@alibaba-inc.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to '')
1 files changed, 16 insertions, 6 deletions
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index c83a1746812f..49dc32c61137 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1598,8 +1598,18 @@ static int soft_offline_huge_page(struct page *page, int flags)
if (ret > 0)
ret = -EIO;
} else {
- if (PageHuge(page))
- dissolve_free_huge_page(page);
+ /*
+ * We set PG_hwpoison only when the migration source hugepage
+ * was successfully dissolved, because otherwise hwpoisoned
+ * hugepage remains on free hugepage list, then userspace will
+ * find it as SIGBUS by allocation failure. That's not expected
+ * in soft-offlining.
+ */
+ ret = dissolve_free_huge_page(page);
+ if (!ret) {
+ if (set_hwpoison_free_buddy_page(page))
+ num_poisoned_pages_inc();
+ }
return ret;
@@ -1715,13 +1725,13 @@ static int soft_offline_in_use_page(struct page *page, int flags)
static void soft_offline_free_page(struct page *page)
+ int rc = 0;
struct page *head = compound_head(page);
- if (!TestSetPageHWPoison(head)) {
+ if (PageHuge(head))
+ rc = dissolve_free_huge_page(page);
+ if (!rc && !TestSetPageHWPoison(page))
- if (PageHuge(head))
- dissolve_free_huge_page(page);
- }