From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8BBD7606A32C for ; Mon, 2 Nov 2026 12:19:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=hzwaB/jU; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Z6X9Wt1f DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc: To:From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Unsubscribe-Post: List-Owner; bh=7aamrL1eeNrbIdMSN+jaXpW6b7pg64KUgg9/NR7r4M8=; b=hzwaB/jU1ohQnp p6xiS/gfSFBW9bhR1Bln/IJ+m7Yn+2f+draS+aRvwj7LaqJ4rPw8X0NHZ6catdeVsJ0DMO63wcDnX O1Js8S7hT6uzU2NnvEhp7CT5iFC72zBsIcBbW73wRQVAdNZdaRFEYOaDOrzUsreXqMrUtPg/qQ2eN +l7fnp3Cc/hA6mDdjweptCiEdQzPJg4SneuXEhGWGHsCNUNrPwNVWuuhe22JGd5DNsXB+UwXFoxKa l0QqFPxeIjqi2/3ekBfe6oRxvpDjlcsTj7iHk69OTgD1eQBL3KLdJQUUhH+VkX1Z0QJetNWcEl4XE bBIRYRDkzDHRTDe5dPBw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xNr0a-0000000GS7F-3Dvz; Mon, 02 Nov 2026 12:19:28 +0000 Received: from out-93.mta0.migadu.com ([2001:41d0:1004:224b::5d] helo=mta0.migadu.com) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xNr0X-0000000GS6S-284C for kexec@lists.infradead.org; Mon, 02 Nov 2026 12:19:26 +0000 X-Envelope-To: kexec@lists.infradead.org DKIM-Signature: a=rsa-sha256; bh=r/y28Pr8KNBr61CZIB3z7msn3ARAQOG25oOo8bDyEqs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793621962; v=1; x=1794226762; b=Z6X9Wt1f2OM0mk9Cvw5ZsBYTsSsI5PkwaBYJjVaRrHKRsTE9x/ymuRWOcLnrF28+pJweuNV7 6EzFPwGVjc92CRJwXYeA37ONO25xqpbqAElMy37M/9RJ7oZUyP837HGQFBUQd7QRrP3u8yb4+GD 5HLS9jSoxykzaPBgfV1a8xbo= X-Envelope-To: kexec@lists.infradead.org Received: by smtp.migadu.com with ESMTPS id c966688054ce713b; Mon, 02 Nov 2026 12:19:21 +0000 X-Mizu-Trace-ID: c966688054ce713b 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, stable@vger.kernel.org, usama.anjum@arm.com Subject: Re: [PATCH v3 31/47] mm/mremap: recheck PUDs under the page table lock Date: Mon, 2 Nov 2026 20:19:14 +0800 Message-ID: <20261102121914.69229-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261031-fixes_core-v3-31-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-31-d6437171ecc3@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261102_041925_747606_73EF00CA X-CRM114-Status: UNSURE ( 8.96 ) X-CRM114-Notice: Please train this message. X-Spam-Score: -2.1 (--) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-13.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Sat, Oct 31, 2026 at 10:40:00AM +0100, David Hildenbrand (Arm) wrote: >Once get_old_pud() is fixed to accept PUD leaves, unmap_mapping_range() can >clear a leaf between the lookup and the move. Holding mmap_lock in write >mode does not prevent this. > >If the zap happens before move_page_tables() tests the entry, an empty >PUD can reach move_normal_pud(), where pud_populate() turns it into a >present page table entry. If it happens after the test, move_huge_pud() >can instead try to move an empty entry, triggering CONFIG_DEBUG_VM >warnings on powerpc. > >Recheck the source under the page table lock in both helpers. Treat an >empty source in move_normal_pud() as a completed move, and use >__pud_trans_huge_lock() in move_huge_pud(). > >In the future we should likely have the code lookup a PUD/PMD lockless >once, instead of multiple times, because one of the problematic bits >here is the: > > pud_trans_huge(*old_pud) > >Fixes: 0881ace292b6 ("mm/mremap: use pmd/pud_poplulate to update page table entries") >Cc: stable@vger.kernel.org >Reviewed-by: Lorenzo Stoakes (ARM) >Reviewed-by: Pedro Falcato >Tested-by: Muhammad Usama Anjum >Signed-off-by: David Hildenbrand (Arm) >--- Reviewed-by: Lance Yang