linux-kernel - [PATCH -next] sched/isolation: Use static_branch_enable_cpuslocked() on housekeeping

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Message-Id: <20260122080902.2312721-1-chenridong@huaweicloud.com>
Date: Thu, 22 Jan 2026 08:09:02 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: longman@...hat.com,
	chenridong@...weicloud.com,
	tj@...nel.org,
	hannes@...xchg.org,
	mkoutny@...e.com,
	mingo@...hat.com,
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	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
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	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	frederic@...nel.org
Cc: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lujialin4@...wei.com
Subject: [PATCH -next] sched/isolation: Use static_branch_enable_cpuslocked() on housekeeping_update

From: Chen Ridong <chenridong@...wei.com>

The warning is observed:

 WARNING: possible recursive locking detected
 6.19.0-rc6-next-20260121 #1046 Not tainted
 --------------------------------------------
 test_cpuset_prs/686 is trying to acquire lock:
 (cpu_hotplug_lock){++++}-{0:0}, at: static_key_enable+0xd/0x20

 but task is already holding lock:
 (cpu_hotplug_lock){++++}-{0:0}, at: cpuset_partition_write+0x72/0x10

 other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(cpu_hotplug_lock);
   lock(cpu_hotplug_lock);

  *** DEADLOCK ***

  May be due to missing lock nesting notation

 stack backtrace:
 CPU: 11 UID: 0 PID: 686 Comm: test_cpuset_prs  6.19.0-rc6-next-20260121 #1
 Call Trace:
  <TASK>
  dump_stack_lvl+0x82/0xd0
  print_deadlock_bug+0x288/0x3c0
  __lock_acquire+0x1506/0x27f0
  lock_acquire+0xc8/0x2d0
  ? static_key_enable+0xd/0x20
  cpus_read_lock+0x3b/0xd0
  ? static_key_enable+0xd/0x20
  static_key_enable+0xd/0x20
  housekeeping_update+0xe7/0x1b0
  update_prstate+0x3f2/0x580
  cpuset_partition_write+0x98/0x100
  kernfs_fop_write_iter+0x14e/0x200
  vfs_write+0x367/0x510
  ksys_write+0x66/0xe0
  do_syscall_64+0x6b/0x390
  entry_SYSCALL_64_after_hwframe+0x76/0x7e
 RIP: 0033:0x7f824cf8c887

The commit 7109b22e6581 ("cpuset: Update HK_TYPE_DOMAIN cpumask from
cpuset") introduced housekeeping_update, which calls static_branch_enable
while cpu_read_lock() is held. Since static_key_enable itself also acquires
cpu_read_lock, this leads to a lockdep warning. To resolve this issue,
replace the call to static_key_enable with static_branch_enable_cpuslocked.

Fixes: 7109b22e6581 ("cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset")
Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 kernel/cgroup/cpuset.c   | 2 --
 kernel/sched/isolation.c | 4 +++-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 392ce795656d..a26ccff55bb7 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1308,8 +1308,6 @@ static void update_isolation_cpumasks(void)
 	if (!isolated_cpus_updating)
 		return;
 
-	lockdep_assert_cpus_held();
-
 	ret = housekeeping_update(isolated_cpus);
 	WARN_ON_ONCE(ret < 0);
 
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index ef152d401fe2..3b725d39c06e 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -123,6 +123,8 @@ int housekeeping_update(struct cpumask *isol_mask)
 	struct cpumask *trial, *old = NULL;
 	int err;
 
+	lockdep_assert_cpus_held();
+
 	trial = kmalloc(cpumask_size(), GFP_KERNEL);
 	if (!trial)
 		return -ENOMEM;
@@ -134,7 +136,7 @@ int housekeeping_update(struct cpumask *isol_mask)
 	}
 
 	if (!housekeeping.flags)
-		static_branch_enable(&housekeeping_overridden);
+		static_branch_enable_cpuslocked(&housekeeping_overridden);
 
 	if (housekeeping.flags & HK_FLAG_DOMAIN)
 		old = housekeeping_cpumask_dereference(HK_TYPE_DOMAIN);
-- 
2.34.1