linux-kernel - [PATCH] cpufreq: drop redundant cpus_read_lock() from store_local

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Message-ID: <20250513015726.1497-1-ImanDevel@gmail.com>
Date: Mon, 12 May 2025 21:57:26 -0400
From: Seyediman Seyedarab <imandevel@...il.com>
To: rafael@...nel.org,
	viresh.kumar@...aro.org
Cc: linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	Seyediman Seyedarab <ImanDevel@...il.com>
Subject: [PATCH] cpufreq: drop redundant cpus_read_lock() from store_local_boost()

Lockdep reports a possible circular locking dependency[1] when
cpu_hotplug_lock is acquired inside store_local_boost(), after
policy->rwsem has already been taken by store().

However, the boost update is strictly per-policy and does not
access shared state or iterate over all policies. Since policy->rwsem
is already held, this is enough to serialize against concurrent
topology changes for the current policy.

Remove the cpus_read_lock() to resolve the lockdep warning and
avoid unnecessary locking.

 [1]
 ======================================================
 WARNING: possible circular locking dependency detected
 6.15.0-rc6-debug-gb01fc4eca73c #1 Not tainted
 ------------------------------------------------------
 power-profiles-/588 is trying to acquire lock:
 ffffffffb3a7d910 (cpu_hotplug_lock){++++}-{0:0}, at: store_local_boost+0x56/0xd0

 but task is already holding lock:
 ffff8b6e5a12c380 (&policy->rwsem){++++}-{4:4}, at: store+0x37/0x90

 which lock already depends on the new lock.

 the existing dependency chain (in reverse order) is:

 -> #2 (&policy->rwsem){++++}-{4:4}:
        down_write+0x29/0xb0
        cpufreq_online+0x7e8/0xa40
        cpufreq_add_dev+0x82/0xa0
        subsys_interface_register+0x148/0x160
        cpufreq_register_driver+0x15d/0x260
        amd_pstate_register_driver+0x36/0x90
        amd_pstate_init+0x1e7/0x270
        do_one_initcall+0x68/0x2b0
        kernel_init_freeable+0x231/0x270
        kernel_init+0x15/0x130
        ret_from_fork+0x2c/0x50
        ret_from_fork_asm+0x11/0x20

 -> #1 (subsys mutex#3){+.+.}-{4:4}:
        __mutex_lock+0xc2/0x930
        subsys_interface_register+0x7f/0x160
        cpufreq_register_driver+0x15d/0x260
        amd_pstate_register_driver+0x36/0x90
        amd_pstate_init+0x1e7/0x270
        do_one_initcall+0x68/0x2b0
        kernel_init_freeable+0x231/0x270
        kernel_init+0x15/0x130
        ret_from_fork+0x2c/0x50
        ret_from_fork_asm+0x11/0x20

 -> #0 (cpu_hotplug_lock){++++}-{0:0}:
        __lock_acquire+0x10ed/0x1850
        lock_acquire.part.0+0x69/0x1b0
        cpus_read_lock+0x2a/0xc0
        store_local_boost+0x56/0xd0
        store+0x50/0x90
        kernfs_fop_write_iter+0x132/0x200
        vfs_write+0x2b3/0x590
        ksys_write+0x74/0xf0
        do_syscall_64+0xbb/0x1d0
        entry_SYSCALL_64_after_hwframe+0x56/0x5e

Signed-off-by: Seyediman Seyedarab <ImanDevel@...il.com>
---
 drivers/cpufreq/cpufreq.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 731ecfc17..759dd178a 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -622,10 +622,7 @@ static ssize_t store_local_boost(struct cpufreq_policy *policy,
 	if (!policy->boost_supported)
 		return -EINVAL;
 
-	cpus_read_lock();
 	ret = policy_set_boost(policy, enable);
-	cpus_read_unlock();
-
 	if (!ret)
 		return count;
 
-- 
2.49.0