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Thu, 29 Oct 2026 04:53:44 +0000 X-Mizu-Trace-ID: 06f3ecca37f8f8d0 X-Migadu-Flow: FLOW_OUT From: xu.xin@linux.dev To: david@kernel.org Cc: akpm@linux-foundation.org, aneesh.kumar@kernel.org, apopple@nvidia.com, axelrasmussen@google.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, baoquan.he@linux.dev, chengming.zhou@linux.dev, chrisl@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, harry@kernel.org, hughd@google.com, jack@suse.cz, jannh@google.com, jgg@ziepe.ca, jhubbard@nvidia.com, josef@toxicpanda.com, joshua.hahnjy@gmail.com, kas@kernel.org, kasong@tencent.com, kees@kernel.org, kexec@lists.infradead.org, lance.yang@linux.dev, liam@infradead.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, matthew.brost@intel.com, mhocko@kernel.org, mhocko@suse.com, minchan@kernel.org, muchun.song@linux.dev, nico.pache@linux.dev, nphamcs@gmail.com, npiggin@gmail.com, osalvador@suse.de, pasha.tatashin@soleen.com, peterx@redhat.com, peterz@infradead.org, pfalcato@suse.de, pratyush@kernel.org, qi.zheng@linux.dev, rakie.kim@sk.com, riel@surriel.com, rppt@kernel.org, ryan.roberts@arm.com, shakeel.butt@linux.dev, shikemeng@huaweicloud.com, stable@vger.kernel.org, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, weixugc@google.com, will@kernel.org, willy@infradead.org, xu.xin@linux.dev, ying.huang@linux.alibaba.com, youngjun.park@lge.com, yuanchu@google.com, ziy@nvidia.com Subject: Re: [PATCH 33/46] mm/madvise: fix data loss from MADV_FREE on a KSM page Date: Thu, 29 Oct 2026 12:53:07 +0800 Message-Id: <20261029045307.131675-1-xu.xin@linux.dev> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20261027-fixes_core-v1-33-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-33-6f74bec9a5bb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3FFD11A0002 X-Stat-Signature: ym4z6oyep6mn7obbe9arh9btx3gz4fwc X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793249626-136955 X-HE-Meta: U2FsdGVkX18YvmDFx3L4YsLyKPW46orTG6UdbRslNRMtfBVCFtZNDkane7vJMgA5bN2DTUV4h/PMdzaWW1SkKzXFfd0L86NEKcN8UQhgU0TS0LNrZtI0IkY2BIM/jxYbwuwUy90sUMDmaQCmmEIMNAIqRU399F1SmwPFHBL+M/dl5vUi1IRelJf3l6afy8rJSpgPViZyVaDp5IycrlvQg1RZas6MxlViK9Xosl3YMo6oIb9ldEJBTRGoy3ko+ywTt/rOEmM9aBrd5muA0+qxoROWXYwetRAx1k4oeKdflnOZHK8Tg/yMKPc1EcVnqT0unXr3YcQRX2+odIsBYBXxa+ld2mMLJMn4PGrtS/6EO59Dyr0lCfJhRkp39S3VqdsmKHEVfZ2ByUkX4LWXiYV9Aa5H7g2ONkDffFVUGfqh7o2x/lLKOVJCVF2jF3DltA36+Vg6TdARkCUjeKlZx+9fzg2kDuyWLpDnuSpvMr39uagLX+jf6oYG5IiOCFHBPG2AT0Y6UV4i3r3Fc6m3TdzXxThsW5BU4Bv1/XzI0Zckuq0348taTkRE0yRRVuma5kch37Xx4DCcvp5zt6j0J3h1V4Z4VZtzzARlu/HVlR3NNxW7eIWKCJU+7EabuQxd80OYe8fOTI2QiHhY0jzqCwYpgFfZbWdsmko3m/dO0uamn/bODUV3ZKGrvPu/91dsJZSncmP6JQdqI7cYkZKgj0IT/KWUSa7oSot2r2UZLe2GdKTd2exat7+hEsDHLkhBLy3WS3D8JbjlyIN5lOJGurPwp0mCQthu1gG0CFV9BtWfBduFrPezSzwrPOAfOH89+Hzj85EC2vuBZxjPUcUuhkbZNG4GlrVaLN7OG7TCSNlIIMa5UryKVbx+ihkEUYhl2+HW19BQBhVq4P/b5uVMMJR23OQWD+QRyWx/wea0L+w7N52Z14fHPkNPVk1odlsqRa2ATXxnXz4GZenwn/Bz8Hq TdvY21gr P3oSd1JWlVpNB7bLIlpadCnJ8gb33Lj0JKveMfQb+t9ne1sWi06KmpPPXecKOmhHF821wgDrw1j1+zkf5SCSBt/HnSgvLM5T8xbu5Vm4HPkfT6uv5v0CiuO4FMmlE8xrIJcn4jbWR9zVh+zyPVWDp16u2sPagvOqHWJQyrdiK9amWOARzvo6w38UMnYmZRRZZl1AhuU3KvqGgczrMJn9JJ6dw4kjHNlkMuWdU5loa6troYymev+27TjOIegsXlAzAd298YzXk3tXtkcw1OfjQ1PzoAbdnuFYhDojW9LFNL8vO4l23eCLONDSkZA5A4V8NiSUKbXEgGpJOZl0Q8GJElj5P0Bcbif50QnroiYJXIwZxngbu5YORq85hsO13g69DNmqPRwS20IAPSQ4tcFSNo75RJLwWG6Gyt1UmhjFeMbM7ljjpoGP0SPfqjQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 > MADV_FREE can clear the dirty flag of a singly mapped KSM folio. The > folio remains in the stable tree and can gain new mappings without being > dirtied again. Once marked lazyfree, reclaim can discard data that those > mappings still need. > > KSM always marks a folio dirty when converting it to a KSM folio in > try_to_merge_one_page(). Marking a folio lazyfree clears PG_swapbacked > but leaves PG_dirty unchanged. Preserving PG_dirty makes reclaim restore > PG_swapbacked instead of discarding the folio. This also protects folios > that were already lazyfree when KSM converted them. > > Skip KSM folios before clearing their dirty flag, checking under the > folio lock to serialize with KSM conversion. > > Fixes: 854e9ed09ded ("mm: support madvise(MADV_FREE)") > Cc: stable@vger.kernel.org > Reported-by: Josef Bacik > Reviewed-by: Lorenzo Stoakes (ARM) > Signed-off-by: David Hildenbrand (Arm) > --- > mm/madvise.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 75b409e97dbf2..a16e3cb256b7b 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -756,6 +756,15 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > if (folio_test_swapcache(folio) || folio_test_dirty(folio)) { > if (!folio_trylock(folio)) > continue; > + /* > + * KSM folios can gain new mappings at any time, so we must > + * not clear their dirty flag. > + */ > + if (folio_test_ksm(folio)) { > + folio_unlock(folio); > + continue; > + } > + > /* > * If we have a large folio at this point, we know it is > * fully mapped so if its mapcount is the same as its > > -- > 2.43.0 The fix looks correct to me: checking folio_test_ksm() under the folio lock properly serializes with KSM conversion, and skipping the folio avoids clearing PG_dirty on a KSM folio. Reviewed-by: Xu Xin