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=1793306697; b=iEhp7TmRivfbvuduI0c8vk3UEAgaB921Urf9VMXjjUFOJcclS3jX2MbhEVV7hCnvZ82V YGhsfBCLYL3DbrolEWFM2OxBxW4FQfsXFvGC/uz6oYYzVRntg+3di77X0fy07hgEGj4GM JuQbZE79aSksqNQhNinw2iFvj7AQ5xGEdj80rxUMNfsqLXFxnHOsynb9rYKj/rSMu/6wA CmvOHyEyoYEV6pGbGvsj9YpJ6vDfc3yBmi2lIpKej1n2xLbpEamw3qLAQjOIs6Qk0gNSP tcbJXiFU8aI0lcTrlR4CJUQYAZjFMC/PzJQB/kWE4IuCjc12hb2s30zpzYpwveFF57A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793306697; 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=0u9mqum51kiy34ukMYiOeDJqgQ6PcqJiGIEfUzDte84=; b=oXXQYZV0gpmoKc3sEZNJ878afSL58eBsSizlqIsAO2iwvFcxkB5rfrQjsu4SvecyUwQh CRJib1NG8TMdW136xBgIkJH/K2JS38WPiDT7uYaGsEWvCMN2+iYaRd1QR5rXtPF7U9aho 86sS5CJEIGIAaoMFn9CebwOrucrYi+b0nmJDCGlwl2MsoO6oEyhSXhMwr/wrR4HrWxAwy /Jx+5n3mSkWpAwDDdm3DtREICvHtylTNQqYVq7wdOiPFVLITWpT5RE/+7QXJoORe7jH1R ASca29qKn2HriDCWw7z28SBDUIVvnXmJrh3nQeuJ2CmE9Q9Jv3N2hWnWuJfkGZywwlA== 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=XNLXlqRw; 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) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9933D60A2615; Thu, 29 Oct 2026 20:44:57 +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=XNLXlqRw Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F9CC1F01824; Thu, 29 Oct 2026 20:44:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793306690; bh=0u9mqum51kiy34ukMYiOeDJqgQ6PcqJiGIEfUzDte84=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=XNLXlqRwdRH7zOXlHSAyM5r9l+ZsOYydF9IM6c41SfzDtPH1QjYiKg2vebUPxLRhE op9syInbMCIbPK5ag5w28kgrB20oq6dz6kz7zwHtoMeI3sn0MMvrWpam94RFGJgDxP PwuSJ2sDX281xB+sF7JbamBjH+Lt1N+zLFvcykhavgdcPfZcysVtAD4MHmB4sYH6Ln ybtI5TkPw6mEClQrIsXfrvgw+3L5rwnHWTSP6EOAsNIyTGyK5uyY2hbH03ERH5/SzU /29GOoPKsf2oq6PwxEHLGhAGPKt6XxH3qiXXHt/UH7EJc+i1SCplW5JPkQ0WQvlUQC DoaDQWsFpWhEA== From: "David Hildenbrand (Arm)" Date: Thu, 29 Oct 2026 21:33:41 +0100 Subject: [PATCH v2 46/47] mm/memory-tiers: unregister empty tiers outside memory_tier_lock X-Mailing-List: linux-arch@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: <20261029-fixes_core-v2-46-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> In-Reply-To: <20261029-fixes_core-v2-0-a64ce7f83abb@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=3065; i=david@kernel.org; h=from:subject:message-id; bh=Be0cEORXL/+FFSLbAGaUCWXPcitw/28TU4MyQxK8Pu4=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIer+2KdjtU9mUqD/ObE6nfr6W/WsvPu0X2p7PUp8V1b +oT/Z1XdZSyMIhxMMiKKbIEBd83ePlyXW21Gx8zzBxWJpAhDFycAjCRk6cYGdakdG50VWY+a/9V 8/mJgoV/fRerH9Bh/RdRvUB9CnvUSjuG/24s+zm964Q1rNsURSvOGhmcdnscZ7DUsWr7it/1S89 +5wYA 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 Reviewed-by: Gregory Price (Meta) 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 25e121851b58..8eda313cf619 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