Handling a memory failure pointing inside a huge page requires splitting the page. The splitting logic uses a mechanism, implemented in migrate.c:try_to_map_unused_to_zeropage(), that inspects contents of individual pages to find zero-filled pages. The read access to the contents may cause a new, synchronous exception like an x86 Machine Check, delivered before the initial memory_failure() finishes, ending in a crash. Luckily memory_failure() already sets the has_hwpoisoned flag on the folio right before try_to_split_thp_page(). Don't enable the shared zeropage mechanism (RMP_USE_SHARED_ZEROPAGE flag) down in __split_unmapped_folio() when the original folio has has_hwpoisoned. Note: we're disabling a potentially useful feature, some of the individual pages that aren't poisoned might be zero-filled. One argument for not trying to add a mechanism to maybe re-scan them later, apart from code cost, is that the owning process is likely being killed and the memory released. Signed-off-by: Andrew Zaborowski --- mm/huge_memory.c | 3 ++- mm/memory-failure.c | 6 ++++-- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9c38a95e9f0..1568f0308b9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3588,6 +3588,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, struct list_head *list, bool uniform_split) { struct deferred_split *ds_queue = get_deferred_split_queue(folio); + bool has_hwpoisoned = folio_test_has_hwpoisoned(folio); XA_STATE(xas, &folio->mapping->i_pages, folio->index); struct folio *end_folio = folio_next(folio); bool is_anon = folio_test_anon(folio); @@ -3858,7 +3859,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, if (nr_shmem_dropped) shmem_uncharge(mapping->host, nr_shmem_dropped); - if (!ret && is_anon) + if (!ret && is_anon && !has_hwpoisoned) remap_flags = RMP_USE_SHARED_ZEROPAGE; remap_page(folio, 1 << order, remap_flags); diff --git a/mm/memory-failure.c b/mm/memory-failure.c index fc30ca4804b..2d755493de9 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -2352,8 +2352,10 @@ int memory_failure(unsigned long pfn, int flags) * otherwise it may race with THP split. * And the flag can't be set in get_hwpoison_page() since * it is called by soft offline too and it is just called - * for !MF_COUNT_INCREASED. So here seems to be the best - * place. + * for !MF_COUNT_INCREASED. + * It also tells __split_unmapped_folio() to not bother + * using the shared zeropage -- the all-zeros check would + * consume the poison. So here seems to be the best place. * * Don't need care about the above error handling paths for * get_hwpoison_page() since they handle either free page -- 2.45.2