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=1793440333; b=qP9SkzxqgQI3kszqIpuBSmIyEN3ESk2iHk0Fsk8cJIUl8EowAsK7Zllj6FS1ons+w1Ku wZsv392MKEyvjO/Mg9d36yB7fUOTQiRGT7442whKelDUiGME52m/knOM91Hyg09aIeHfV HvkYOGNnodSMrU5icMETRSo/DgpqOLekfhW6VHNzUPFAXoQSXaX1CYY3fATFmosPuw75/ 3An7EHqnXxHJRqYOA5mlxngdL0znULlZvTh8XVsj3fpus3IoCx2qny/dMutK71FX1TeiO dLyDGuCxp/CcEQxNAMyWlrI0MkCUF08M0yY07tcAi/oUwlRQ593LBg9MHi8iY2zA7uA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793440333; 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=LXWsGGAuGYMpNthZzj7j0qIEhHCnCLdw4tDv3Dde7tU=; b=pGfNY/QbPia0FakNl1uRPS13fpbEyTru7GFXcT8shxYQRgPTmjJ48D0xOcYasrje2V+F n1bDHZnkwGK0lIf54VRHF3XaFjldUi5bYK826d3UmIRzi/QHoAJIzHZVqjCy2FW1ytgpa w+jsRIeMXLZ+oWbl9pJAwLZTXB3WRdgd93lpbRdOChKggeNVUPNixIc0sW9HH0nCvJjiS yXPlffp31mDh43lHert6n2i9l309dihDFElvDwy5FBkc8GVUuZpAE3K3ymtTx1zWMzJ+r ALSmCNHbCH0z56aC2MROpe/fNinsSrlbnIIoJi3b0cMfPeCrRigL/bXmguwS2kqaimg== 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=WDaRfZV8; 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 CACD5606A31E; Sat, 31 Oct 2026 09:52:12 +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=WDaRfZV8 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99D3F1F00919; Sat, 31 Oct 2026 09:51:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793440332; bh=LXWsGGAuGYMpNthZzj7j0qIEhHCnCLdw4tDv3Dde7tU=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=WDaRfZV8lrdSHWo2bJPjhRAvbOAWGSBSNWe8J3upHnl+8qcyY3Ce8G7dfUa1DjNu8 H8f+FSaHVuGPPNLccj7ytAj3BCbt3FdYbeSSKQF/QvfRjblvOsaNaGnbw9hLcvhcsJ dDRBr8BfUwDlVj32RVLLIYvP7S3lEAMUk4hAgnS3bHgLHai9rCoFXH1JhD19+t2mMl n7zx2EBIckhQ3seuwiWQtQn9Jl0jqIz4d6PcM9b+vRYVjFs35sap3cB26D91h0RaDe MOMYNkE9tGqvEbueSr3By16YiV7Ok4fX4v3f6g5/bvzabRudn/+qA5QxL3Z0bM3mj6 nFye94PFipthw== From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:40:15 +0100 Subject: [PATCH v3 46/47] mm/memory-tiers: unregister empty tiers outside memory_tier_lock X-Mailing-List: linux-fsdevel@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: <20261031-fixes_core-v3-46-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> In-Reply-To: <20261031-fixes_core-v3-0-d6437171ecc3@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 , Muhammad Usama Anjum , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3122; i=david@kernel.org; h=from:subject:message-id; bh=4kChVYvvx74BRlmNy9r2/KDpSY0XvvEjaE2NRYfL7Rw=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLKebs9+99iyuX3mtNxzRav077QJloZ+YyoR6Cgy2vp4d YX/5CM6HaUsDGIcDLJiiixBwfcNXr5cV1vtxscMM4eVCWQIAxenAEzk4SaGf/ZLKmUk1xgsDAxl Pc3A+6Vf/4kPc5PbSzOWCXdu2uiXVTAyrOyZI/RJ5uh8YRfxXwU8K8t/sD5yzZZddPjK5FOzcxM mMQAA 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) Tested-by: Muhammad Usama Anjum 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