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=1794273244; b=b1D7vJA/mbdkqssXn1cryeBzKRoiLS4TBb4BMjlVuGvy5LlPJJVCDdz6Oe7npkrjB9ac +4UvgUvfh4gx+suSlF2C6MAR/cMHHSQhNHCNgInGdXiX6PLv6IodFQuqYCPw3JiRawX9f Sg8L1YII169KHPXXD1gNYGDvEMLmA1vUbesH1Ks4HPWsF4ACWChlB591PBuNMmSChv4Kd mEZ+Fc9RAVp58C1NFFOhEM/UGpWNZE2gaOdjgZbYpqX4PO29posq53nv6rGah5I24AOBd ZzOhEBKrSflztMPUW9yud+aHApeCDAqOnXJ4lvkuLtwe8i0ijuryeE+am0G6YTb0mLA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794273244; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=b4GqD33bDgG2jSeoAtBIBYkAngMpRaCIfPvaTq5DS3w=; b=eMpAeF4AqBuNo5fJLo1oEYKLzhNjQpq4VRCHpkMFFvFACPgSvMBDtzWQBf2K9q+TkJUQ xoDyV0ihylZaa0HI0S1E0ZPzeGffLqi/A+moEUCRTwH0Y3QozFJRATR3XkzDHtKrIKPhm CA6NegFlSNzD148LoB+hZ3vXNcShguyMqhCuWa/8euqsnrre/QRpR0Ir1jIW9+Pqs5ssS m+zL6n3g5xftPXDIBoi6Rsm5SmZUubiB2Ps31eQDVXvAVFA/Uf/wtqN+z/NUdpdC7G7Tz bFa22HbeK7CPiq6j5G3W6q7bIIY997przxB05Cv0P1eMYvWVSIF26VOXjW/FmjwrWrQ== 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=C05Vbqdf; 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 218FE606A31C for ; Tue, 10 Nov 2026 01:14:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=C05Vbqdf Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E86B1F0089F; Tue, 10 Nov 2026 01:14:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794273244; bh=b4GqD33bDgG2jSeoAtBIBYkAngMpRaCIfPvaTq5DS3w=; h=From:To:Cc:Subject:Date; b=C05VbqdfF+ZmP+AI3xpromn/QSe/cMfItvwtijzszty6e4i1wkpvQSHIeLSsK/o6e aoXSkN4dg8W/EoJ8v+QgtJ2i/lFR4lu20dbbd5gWY6fCXfpi7QHiAcFl8NT+hZH1uj hQaIhsEsbR8p4ePdgT7i/tVfVOJCG59nRHnoq2jmkBBtF9ZlkdAJRMRS+BRUYC0gKP z4RUoQCNm4GO8hwvmUf+9CQ1KB9zTsOLkmYKdjd3Z1z9QIuR0P7v+ndZYtpIV86p25 XQJ7b6BxH4clFQPcIJRorBxaokYN77JKb77ag3xLRcD9QI5AR7Tqbe4i0tpIjG3iU0 Q8dUrBD+TgXlA== From: Sasha Levin To: david@kernel.org, josef@toxicpanda.com, gourry@gourry.net, usama.anjum@arm.com Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mm/memory-tiers: unregister empty tiers outside memory_tier_lock" failed to apply to 6.6-stable tree Date: Mon, 9 Nov 2026 20:14:02 -0500 Message-ID: <20261109201402-failed-6.6-500624f28eca@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@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: 8bit The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 500624f28eca441e35f978979ccfb373202fefd3 # git commit -s git send-email --to '' --in-reply-to '20261109201402-failed-6.6-500624f28eca@kernel.org' --subject-prefix 'PATCH 6.6.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 500624f28eca441e35f978979ccfb373202fefd3 Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:40:15 +0100 Subject: [PATCH] mm/memory-tiers: unregister empty tiers outside memory_tier_lock 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 Link: https://patch.msgid.link/20261031-fixes_core-v3-46-d6437171ecc3@kernel.org 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); -- 2.53.0