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bh=MiW8Mroe3U2+fZ+1bplzdhcNfTtvPuhlvwZ0rPfG9Ps=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793598159; v=1; x=1794202959; b=UuwuZrpRkQYutb58GVikL5ByJkdXkY5hrZ320Ad6t9zbKbpIWUeWtzUj6e7jA2gUDGMoLrrH gUeLCTBMp061JCHx6Qhx3sjIJSwh8MQzoBlRonU4eD5oEI2+kpHt3ULEzO6l5PK/syFv0vJ1f4r DZ12u63g6acTOpq0688ukOGg= X-Envelope-To: linux-cxl@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 9704e208af575192; Mon, 02 Nov 2026 05:42:37 +0000 X-Mizu-Trace-ID: 9704e208af575192 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, ljs@kernel.org, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, baolin.wang@linux.alibaba.com, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kees@kernel.org, peterz@infradead.org, jannh@google.com, pfalcato@suse.de, hughd@google.com, pasha.tatashin@soleen.com, pratyush@kernel.org, willy@infradead.org, jack@suse.cz, ziy@nvidia.com, lance.yang@linux.dev, riel@surriel.com, harry@kernel.org, apopple@nvidia.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, jhubbard@nvidia.com, peterx@redhat.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, osalvador@suse.de, minchan@kernel.org, muchun.song@linux.dev, xu.xin@linux.dev, chengming.zhou@linux.dev, chrisl@kernel.org, shikemeng@huaweicloud.com, nphamcs@gmail.com, youngjun.park@lge.com, gourry@gourry.net, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, jgg@ziepe.ca, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, josef@toxicpanda.com, stable@vger.kernel.org, usama.anjum@arm.com Subject: Re: [PATCH v3 16/47] mm/khugepaged: fix PMD table lock leak in try_collapse_pte_mapped_thp() Date: Mon, 2 Nov 2026 13:42:32 +0800 Message-ID: <20261102054232.36829-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261031-fixes_core-v3-16-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-16-d6437171ecc3@kernel.org> X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Sat, Oct 31, 2026 at 10:39:45AM +0100, David Hildenbrand (Arm) wrote: >From: Josef Bacik > >For a private mapping with userfaultfd, try_collapse_pte_mapped_thp() >takes the PMD table lock before it maps the page table for the second time. >If that (pte_offset_map_rw_nolock) fails, because the page table vanished >in the meantime due to concurrent page table reclaim, it leaves through >the abort label, where the PMD table lock is unlocked if it differs from >PTE table lock. > >In case the PMD table lock and the PTE table lock match, which is the >case without CONFIG_SPLIT_PTE_PTLOCKS after pte_offset_map_rw_nolock() >failed, we miss to unlock the PMD table. > >To fix it, forget the PTE table lock when we unmap+unlock the PTE table. > >Fix generated by an LLM and sent by Josef Bacik in private. > >Fixes: 6375e95f381e ("mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)") >Cc: stable@vger.kernel.org >Signed-off-by: Josef Bacik >[ david: move the ptl = NULL handling; rewrite description, drop wrong comments ] >Reviewed-by: Gregory Price (Meta) >Tested-by: Gregory Price (Meta) >Tested-by: Muhammad Usama Anjum >Signed-off-by: David Hildenbrand (Arm) >--- Reviewed-by: Lance Yang