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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=d3K6pDSF; 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 29AE4606A324; Tue, 3 Nov 2026 15:00:56 +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=d3K6pDSF Received: by smtp.kernel.org (Postfix) with ESMTPSA id 423AF1F000C1; Tue, 3 Nov 2026 15:00:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793718056; bh=bA0DUmnnxVPUL6fKcA1U0PeMmih16OqQLXC+FqdAHTU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=d3K6pDSFh52zVCjIc/hBdsflRe5uFDEz0Fmn1nI+IKthHiXVq1OjvLBo8PS8Y7GfJ L6G5tw9QmaAoflgCwnDY08eRL/Ga120L9Q1f7tOGn94gVVV4Zdt/sQyCLyuZhP3Mxp UmONMR9peZ0sBrCDpOCrPthNxS+XUm5DPf7OZLwL9Rv3d3KK7VGugZs6A3VMEANKa9 OivpMxXoXJ/30qchLqIfmTlrvWU2x1m87FS8C82zMIbmuXeYq2tYTDcslOIE+U1x35 BgtTY9XjTURfxoHL+kKtzxrdkdqBnO9Ub7CK+2Z0a/9pA6XNBVVaMuIH942o52QY1U aLWb9/Wg3nTbA== Message-ID: Date: Tue, 3 Nov 2026 16:00:45 +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 v5 07/12] mm/mmzone: read each zoneref slot once when filtering by nodemask Content-Language: en-US To: Zi Yan , "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, baolin.wang@linux.alibaba.com, rientjes@google.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, muchun.song@linux.dev, osalvador@suse.de, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, bigeasy@linutronix.de, clrkwllms@kernel.org, nathan@kernel.org, ndesaulniers@google.com, morbo@google.com, justinstitt@google.com, Bessel.Wang@huawei.com, jiang.liu@huawei.com, mgorman@techsingularity.net, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20261101021340.2251928-1-gourry@gourry.net> <20261101021340.2251928-8-gourry@gourry.net> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/3/26 04:01, Zi Yan wrote: > On Sat Oct 31, 2026 at 10:13 PM EDT, Gregory Price (Meta) wrote: >> __next_zones_zonelist() tests a slot's zone for NULL, then reads the >> slot again to look up the zone's node. Offlining a zone's last block >> rebuilds the zonelists in place, so the second read can return the >> terminator: >> >> CPU 0 CPU 1 >> __next_zones_zonelist(nodemask) >> zonelist_zone(slot 1) = NORMAL >> offline_pages() >> build_all_zonelists() >> [MOVABLE, NORMAL, NULL] >> -> [NORMAL, NULL] >> zref_in_nodemask(slot 1) >> zone_to_nid(NULL) >> >> Current GCC and clang merge the two reads, but nothing requires it. >> With mm/mmzone.o built with -fno-inline -fno-ipa-sra, holding a >> nodemask allocation between the reads while the node's last movable >> block goes offline oopses every time: >> >> BUG: kernel NULL pointer dereference, address: 0000000000000060 >> RIP: 0010:zone_to_nid+0x0/0x10 >> Call Trace: >> zref_in_nodemask+0x9/0x20 >> __next_zones_zonelist+0x23/0x70 >> prepare_alloc_pages.constprop.0+0x16c/0x190 >> __alloc_frozen_pages_noprof+0xaf/0x330 >> >> Read the slot once and test that zone. A NULL zone still ends the walk. > > It is better to spell out the rename from zref_in_nodemask() to > zone_in_nodemask(). Added: To achieve that, rename zref_in_nodemask() to zone_in_nodemask() and pass a zone instead of zoneref pointer. > >> >> 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) >> --- >> mm/mmzone.c | 11 ++++++----- >> 1 file changed, 6 insertions(+), 5 deletions(-) >> > > Makes sense. > > Reviewed-by: Zi Yan > >