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Received: from 30.246.104.96(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X6OzcpQ_1783299924 cluster:ay36) by smtp.aliyun-inc.com; Mon, 06 Jul 2026 09:05:25 +0800 Message-ID: <2b7d965d-8079-431a-bb01-2f722eb02c47@linux.alibaba.com> Date: Mon, 6 Jul 2026 09:05:23 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] userfaultfd: wait on source PMD during UFFDIO_MOVE To: Usama Arif , Andrew Morton , baohua@kernel.org, david@kernel.org, dev.jain@arm.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, npache@redhat.com, ryan.roberts@arm.com, ziy@nvidia.com, aarcange@redhat.com, shakeel.butt@linux.dev, hannes@cmpxchg.org, riel@surriel.com, kernel-team@meta.com Cc: sashiko-bot References: <20260705131231.1499198-1-usama.arif@linux.dev> From: Baolin Wang In-Reply-To: <20260705131231.1499198-1-usama.arif@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 600C712000C X-Stat-Signature: n881tpcnrpe5y19d8p3ho1hhfx58szt7 X-Rspam-User: X-HE-Tag: 1783299930-704887 X-HE-Meta: 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 y1hLNN8D hQmv4PImGbI+e5ynpkBYTSMq7UymY7K1Pb1TxEJXOD692TipNqPU8Ao7BJy1y33BzArmbdpJY6RwzamvzFY+R6vioB8jsTe0RjH1swbICfVuGP2tKwQij6Jc9Y/7cYpHcbRXdT9Bt6bT2tS2/4RJZV2Tl8X9RaNoKD0iCWpte+P1CD6fs8BTp/TFG5/l796WYpjmGTd3Qv4bLELxBsSRFqMsmuvU8sTL5eflEsFFhMtZfoC68PTRKX9qXCtyxkcbsRZyC5kUteQfamHmbcLzQsbGzR78uhvE0Nbk+DLoljBx2NPDnMN6R+ZRj2Pg45NOQYcE6asERPf6gP6yqRTOqc7w7DmmtadT6jyQE+pRlZQRjjmz3z4HS9+3uIcgnuabyV/gL5wbFU2yPD0KH6LdcGYN77jSs1jUAwaHG5Pggd5P3ahJ30gVuAYw3uA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/5/26 9:12 PM, Usama Arif wrote: > move_pages_huge_pmd() snapshots src_pmdval under src_ptl, drops the lock, > and, for migration entries, waits with pmd_migration_entry_wait(). > > Passing &src_pmdval is wrong. pmd_migration_entry_wait() must lock and > re-read the real page-table PMD; on split-PMD-lock kernels, a stack > address also resolves to the wrong lock. softleaf_entry_wait_on_locked() > then waits without a folio reference, which is safe only while serialized > against migration-entry removal by the real PT lock. > > Pass src_pmd, matching __handle_mm_fault() and hmm_vma_walk_pmd(). > > Reported-by: sashiko-bot > Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=8 > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") > Signed-off-by: Usama Arif > --- Good catch. Agree with Andrew that we should cc stable. Reviewed-by: Baolin Wang