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Tue, 16 Sep 2025 09:01:36 -0700 (PDT) From: Kairui Song To: linux-mm@kvack.org Cc: Kairui Song , Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , Barry Song , Baoquan He , Nhat Pham , Kemeng Shi , Baolin Wang , Ying Huang , Johannes Weiner , David Hildenbrand , Yosry Ahmed , Lorenzo Stoakes , Zi Yan , linux-kernel@vger.kernel.org, Kairui Song Subject: [PATCH v4 04/15] mm, swap: check page poison flag after locking it Date: Wed, 17 Sep 2025 00:00:49 +0800 Message-ID: <20250916160100.31545-5-ryncsn@gmail.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250916160100.31545-1-ryncsn@gmail.com> References: <20250916160100.31545-1-ryncsn@gmail.com> Reply-To: Kairui Song Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Kairui Song Instead of checking the poison flag only in the fast swap cache lookup path, always check the poison flags after locking a swap cache folio. There are two reasons to do so. The folio is unstable and could be removed from the swap cache anytime, so it's totally possible that the folio is no longer the backing folio of a swap entry, and could be an irrelevant poisoned folio. We might mistakenly kill a faulting process. And it's totally possible or even common for the slow swap in path (swapin_readahead) to bring in a cached folio. The cache folio could be poisoned, too. Only checking the poison flag in the fast path will miss such folios. The race window is tiny, so it's very unlikely to happen, though. While at it, also add a unlikely prefix. Signed-off-by: Kairui Song Acked-by: Chris Li Acked-by: David Hildenbrand Acked-by: Nhat Pham --- mm/memory.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 10ef528a5f44..94a5928e8ace 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4661,10 +4661,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) goto out; =20 folio =3D swap_cache_get_folio(entry); - if (folio) { + if (folio) swap_update_readahead(folio, vma, vmf->address); - page =3D folio_file_page(folio, swp_offset(entry)); - } swapcache =3D folio; =20 if (!folio) { @@ -4735,20 +4733,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) ret =3D VM_FAULT_MAJOR; count_vm_event(PGMAJFAULT); count_memcg_event_mm(vma->vm_mm, PGMAJFAULT); - page =3D folio_file_page(folio, swp_offset(entry)); - } else if (PageHWPoison(page)) { - /* - * hwpoisoned dirty swapcache pages are kept for killing - * owner processes (which may be unknown at hwpoison time) - */ - ret =3D VM_FAULT_HWPOISON; - goto out_release; } =20 ret |=3D folio_lock_or_retry(folio, vmf); if (ret & VM_FAULT_RETRY) goto out_release; =20 + page =3D folio_file_page(folio, swp_offset(entry)); if (swapcache) { /* * Make sure folio_free_swap() or swapoff did not release the @@ -4761,6 +4752,15 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) page_swap_entry(page).val !=3D entry.val)) goto out_page; =20 + if (unlikely(PageHWPoison(page))) { + /* + * hwpoisoned dirty swapcache pages are kept for killing + * owner processes (which may be unknown at hwpoison time) + */ + ret =3D VM_FAULT_HWPOISON; + goto out_page; + } + /* * KSM sometimes has to copy on read faults, for example, if * folio->index of non-ksm folios would be nonlinear inside the --=20 2.51.0