From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793057522; b=rXLyfbmIPUBz0qgDKf2QRsLSH8q/fCVgaY+1Hmk5+q1VmPp23uQDIECPaRgZO5pdIklM YRI/8VLJq6BUyoinFWma4jWwxEJZc5VRsogNcNr0DwPPeV5EJXTq0Ccc8lyhyfjnt9QgN RN669sF+PkBmQ7h/fvvLBpFrfwGKo7IVBNDRZDahx0fBudDStWcb9NYHTpWktNZeTj57A w6PDznYmXjeHr6r4N9GJwqJcJG21B2iPkvP/Fbnf10K2MyvK1YNm5Lm5VsS3ImdZZ5w4A 3AjjuckMhzW0unytD0DhN2F3eETvGk65CwckpxzJjJT3KuC/W00fCeIpWoGCct0lRSg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793057522; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=g9Kj7YHK/vFxzWo8upMpJmyx4xo85TgB6aMFH+6OL8o=; b=YOwlpLIK9ubRRckUMIVpE2wwjKoqd5kvTY1lVgkac96bCTggQ8Ok0oysfeRQL689CA0A L9Jmr80n5hUSTXa2O/o2tVun0Rgjr9YCigZM4xw1eJwMEyVJZpdj+KG9ZGxn7k2bouovy hsg0T0PiZiuzyfAn/TRH7wVz4w/9XkO2TN9aZM/X/hUKQUEaq0W7qVvevxXvtWUdcxXVR xr0h3hFdJx5cl4rMGwN9CDqC/IimVBKFmZuruSdLycKzR7+ZwK3kNrHblPJdEd7YfJRT8 jp6BNPNffsvK5/8oT8ldpCteo6P/k4RaAEzVTUOnsvMNMz6cKaEz7tZuMLCA3YTq2Gg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=eAAUXl2F; 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 4FE73606A31A; Mon, 26 Oct 2026 23:32:02 +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=eAAUXl2F Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE89B1F031E4; Mon, 26 Oct 2026 23:31:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793057522; bh=g9Kj7YHK/vFxzWo8upMpJmyx4xo85TgB6aMFH+6OL8o=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=eAAUXl2Fv5GKOM7MwK2afRhIql+v43hRuiFMsyyr826M/I0/zzX/QoAh89jifpJfI v1h87y90NWXH3G+Skzk7UcVX4m3g3W4YHwjNgyjd1Yaz5yU7aCb1icJ13Nw+U1wmtC Kb9RPkFR6vXSasTDqyogu8qGQbl7zk76Oiidwg8y6E6VzRx8gz2T+JVilpLvNDInzx +Zmhjhsml8/Ry5oByyop5y5ViyFWiKeH7hMIwSBTkt/4jAvpuzZclQPR9gbx2V20Fq vxrSN8N7qWPJWt8kOP6NEIqNU2YHlqBg2gQLZPUGq+HOSPkTNLbGXDN2OooFguG9xB UACjYB1hhSFiQ== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 00:18:05 +0100 Subject: [PATCH 45/46] mm/memory-tiers: unregister empty tiers outside memory_tier_lock 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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261027-fixes_core-v1-45-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> In-Reply-To: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> To: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: 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, Josef Bacik , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3012; i=david@kernel.org; h=from:subject:message-id; bh=GK45sNqq0Okgc4Cym/ZaeHTnABd3IPthztUBcQAaOBo=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLu35/ZcGvOxE3d+ff7dizU7jP4xcLXfbkjrCPlkSC/7 q0Q3ZawjlIWBjEOBlkxRZag4PsGL1+uq61242OGmcPKBDKEgYtTACZy5xUjw62fZi37JRqEY+Ib Lk0qWXgm7vexr8nCzbWyW2aL835eBVRxQWB6qu8u76sSvi8rXlfHO6RcNZv/5OTSWYdiGsNEP/t xAgA= X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A When offlining a node's last memory empties its tier, clear_node_memory_tier() calls device_unregister() while holding memory_tier_lock. A concurrent sysfs read can hold a kernfs active reference and block in nodelist_show() on that mutex. device_unregister() then waits in kernfs_drain() for the read to finish and release its active reference, while the reader waits for the offlining task to release the mutex. Return the node's former tier from clear_node_memory_tier(), making the helper more similar to set_node_memory_tier(), which also returns a memory_tier pointer. Let the caller unlink an empty tier under memory_tier_lock before rebuilding demotion targets, then unregister its device after dropping the lock. Fixes: 9832fb87834e ("mm/demotion: expose memory tier details via sysfs") Cc: stable@vger.kernel.org Reported-by: Josef Bacik Signed-off-by: David Hildenbrand (Arm) --- mm/memory-tiers.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-) diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c index 25e121851b586..8eda313cf6192 100644 --- a/mm/memory-tiers.c +++ b/mm/memory-tiers.c @@ -572,21 +572,14 @@ static struct memory_tier *set_node_memory_tier(int node) return memtier; } -static void destroy_memory_tier(struct memory_tier *memtier) +static struct memory_tier *clear_node_memory_tier(int node) { - list_del(&memtier->list); - device_unregister(&memtier->dev); -} - -static bool clear_node_memory_tier(int node) -{ - bool cleared = false; pg_data_t *pgdat; struct memory_tier *memtier; pgdat = NODE_DATA(node); if (!pgdat) - return false; + return NULL; /* * Make sure that anybody looking at NODE_DATA who finds @@ -604,14 +597,10 @@ static bool clear_node_memory_tier(int node) synchronize_rcu(); memtype = node_memory_types[node].memtype; node_clear(node, memtype->nodes); - if (nodes_empty(memtype->nodes)) { + if (nodes_empty(memtype->nodes)) list_del_init(&memtype->tier_sibling); - if (list_empty(&memtier->memory_types)) - destroy_memory_tier(memtier); - } - cleared = true; } - return cleared; + return memtier; } static void release_memtype(struct kref *kref) @@ -884,13 +873,21 @@ static int __meminit memtier_hotplug_callback(struct notifier_block *self, { struct memory_tier *memtier; struct node_notify *nn = _arg; + bool empty = false; switch (action) { case NODE_REMOVED_LAST_MEMORY: mutex_lock(&memory_tier_lock); - if (clear_node_memory_tier(nn->nid)) + memtier = clear_node_memory_tier(nn->nid); + if (memtier) { + empty = list_empty(&memtier->memory_types); + if (empty) + list_del(&memtier->list); establish_demotion_targets(); + } mutex_unlock(&memory_tier_lock); + if (empty) + device_unregister(&memtier->dev); break; case NODE_ADDED_FIRST_MEMORY: mutex_lock(&memory_tier_lock); -- 2.43.0