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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=dNBXzeZb; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 577DA606A31A; Thu, 29 Oct 2026 15:21:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=dNBXzeZb Received: by smtp.kernel.org (Postfix) with ESMTPSA id C02AB1F01816; Thu, 29 Oct 2026 15:21:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793287297; bh=B+9rlXcZZ8g+5YiYdei6kbu9KZrhPovwLjwJuy+h7zs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=dNBXzeZbES6os+Zzxui4Zil8McbII2bpInSLLpLPFqT3WfE1SIJWJYlObDU+BBTZK Gh6iiURODXPC1QRKVZDzmn3d2LU4ytwmxhfM/FyYPCluGvotplbNmJDiavNEB8BxZg +1SrGz6edGBVHkAxzh1yNgQ7GXB6jzVpbOKR0CruZsbG8blRbZUgNhMuMqVMLZ0upW 4DaKpkJS0gyDiFy/06rFV5JRjs+2lcqXcfUoeBtt+BpZ8bI6wKGaV3VinksrsvCJN3 kfTb1LDe3Ksd2U5r0eca1UJBICmH8/eRDhOGgTcpzj34W5HOSotrHSBF93Iu877Z8i W2csXA5IB2N2w== Message-ID: Date: Thu, 29 Oct 2026 16:21:31 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/8] mm/page_alloc: snapshot the preferred zone against shrink rebuilds Content-Language: en-US To: "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, mgorman@techsingularity.net, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20261028211930.3504634-1-gourry@gourry.net> <20261028211930.3504634-4-gourry@gourry.net> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/28/26 22:19, Gregory Price (Meta) wrote: > get_page_from_freelist() and alloc_pages_bulk_noprof() reread > ac->preferred_zoneref->zone at every use. Offlining a zone's last block > rebuilds the zonelists in place, and the shrunk list's NULL terminator > can land on the preferred slot mid-walk: > > CPU 0 CPU 1 > get_page_from_freelist(GFP_KERNEL | __GFP_THISNODE) > zone = NORMAL (slot 1) > offline_pages() > build_all_zonelists() > [MOVABLE, NORMAL, NULL] > -> [NORMAL, NULL] > rmqueue(zonelist_zone(slot 1), zone) > zone_statistics(NULL, zone) > > BUG: kernel NULL pointer dereference, address: 0000000000000060 > RIP: 0010:get_page_from_freelist+0x6a5/0x15f0 > Call Trace: > __alloc_frozen_pages_noprof+0x125/0x330 > > Read the slot once. Zones are never freed, so a stale zone is safe, and > a NULL slot fails the same way as walking off the end. > > Fixes: 11cd8638c37f ("mm, page_alloc: remove stop_machine from build_all_zonelists") > Cc: stable@vger.kernel.org > Signed-off-by: Gregory Price (Meta) Reviewed-by: Vlastimil Babka (SUSE)