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b=Ke/TbykmgbT+gud/+G2OUkea8+LhLcc0w6t4NzXXLvVJgqkOy70RxPsPyBAXimlHeIx9q4FfNWiBn9aPcfYybw6ixNGE6E3oeWCQdI1dDLRRZpVy5xbQ3RUhaOrTv13HKriVnjtd7X23y0C4Ev648eNDeO3UOqBEEs0IPIccWd8= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037009110;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0XCKvm76_1791440411; Received: from 30.74.144.149(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XCKvm76_1791440411 cluster:ay36) by smtp.aliyun-inc.com; Thu, 08 Oct 2026 14:20:11 +0800 Message-ID: Date: Thu, 8 Oct 2026 14:20:10 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/khugepaged: flush deferred unmaps before dropping a failed folio To: Kyle Zeng , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Zi Yan , outbounddisclosures@openai.com, stable@vger.kernel.org References: <20261007041001.43181-1-kylebot@openai.com> From: Baolin Wang In-Reply-To: <20261007041001.43181-1-kylebot@openai.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6BEAE1C000B X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: d1e1eb16wfzgujjy7nh6a9b7oc43umq4 X-HE-Tag: 1791440418-732001 X-HE-Meta: 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 KsIsl57V pUZAXt0DsoTHNCyN5nX5whUmNQcl5iJRMbCa/dD4vH/f2OgMwv94x6psnuy2w732zEfQdFJ/zhWk5cBVCxi0nYmmD+hYihGQ+GHQ6VQCfFXEWiFT5LmRYpf4MNI3BpyfUvcezRpnASZDq5MHniE3EGjSqUQg0Bc29hzQYDJgmsk+LaxqJ4apw6c5ukuRfaZIN+PZbeWUTdDZ+pi+T6OtZ6lkAygm07I3XqExbcRSaCxBrH9GLI+P+LVNtxcgCHcM851DUQPsCOC8MBzUJKj6EXBmT0OVY+95PVfFK2eodtUPzMy3DOuCzI0JLP3+E42fSKxJMdiBkYWmVR3/4dJui1LlrSyyZOKZYz4mb Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/7/26 12:10 PM, Kyle Zeng wrote: > collapse_file() can fail its reference-count or dirty-folio check after > unmapping with TTU_BATCH_FLUSH. Both paths put back the isolated folio, > then unlock it and drop the lookup reference before reaching the common > try_to_unmap_flush(). > > The page-cache reference does not keep the folio stable once the lock is > released. Another collapse can replace and free it. With its PTEs > already gone, that collapse cannot flush the first task's per-task TLB > batch, and retract_page_tables() skips short or unaligned VMAs. A CPU > can therefore retain a user translation to the freed folio. This has > been reproduced with unprivileged MADV_COLLAPSE on a memfd. > > Flush at out_unlock while the lookup reference and folio lock are still > held. The common flush continues to cover the accumulated pagelist on > both success and rollback, preserving batching on successful collapses. > > Fixes: 6d9df8a5889c ("mm/thp: collapse_file() do try_to_unmap(TTU_BATCH_FLUSH)") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Kyle Zeng > --- Good catch. LGTM. Reviewed-by: Baolin Wang