linux-kernel - [PATCH] cpufreq: fix locking order in store_local

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Message-ID: <20250428043356.3169-1-ImanDevel@gmail.com>
Date: Mon, 28 Apr 2025 00:33:56 -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: fix locking order in store_local_boost to prevent deadlock

Lockdep reports a possible circular locking dependency[1] when
writing to /sys/devices/system/cpu/cpufreq/policyN/boost,
triggered by power-profiles-daemon at boot.

store_local_boost() acquires cpu_hotplug_lock *AFTER* policy->rwsem
has already been taken by the store() handler. However, the expected
locking hierarchy is to acquire cpu_hotplug_lock before policy->rwsem.
This inverted lock order creates a *theoretical* deadlock possibility.

Take cpu_hotplug_lock in the store() before down_write(&policy->rwsem),
and remove the internal cpus_read_lock/unlock pair
inside store_local_boost().

 [1]
 ======================================================
 WARNING: possible circular locking dependency detected
 6.15.0-rc3-debug #28 Not tainted
 ------------------------------------------------------
 power-profiles-/596 is trying to acquire lock:
 ffffffffb147e910 (cpu_hotplug_lock){++++}-{0:0}, at: store_local_boost+0x6a/0xd0

 but task is already holding lock:
 ffff9eaa48377b80 (&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+0x841/0xa00
        cpufreq_add_dev+0x71/0x80
        subsys_interface_register+0x14b/0x170
        cpufreq_register_driver+0x154/0x250
        amd_pstate_register_driver+0x36/0x70
        amd_pstate_init+0x1e7/0x270
        do_one_initcall+0x67/0x2c0
        kernel_init_freeable+0x230/0x270
        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+0x83/0x170
        cpufreq_register_driver+0x154/0x250
        amd_pstate_register_driver+0x36/0x70
        amd_pstate_init+0x1e7/0x270
        do_one_initcall+0x67/0x2c0
        kernel_init_freeable+0x230/0x270
        kernel_init+0x15/0x130
        ret_from_fork+0x2c/0x50
        ret_from_fork_asm+0x11/0x20

 -> #0 (cpu_hotplug_lock){++++}-{0:0}:
        __lock_acquire+0x1087/0x17e0
        lock_acquire.part.0+0x66/0x1b0
        cpus_read_lock+0x2a/0xc0
        store_local_boost+0x6a/0xd0
        store+0x50/0x90
        kernfs_fop_write_iter+0x135/0x200
        vfs_write+0x2ab/0x540
        ksys_write+0x6c/0xe0
        do_syscall_64+0xbb/0x1d0
        entry_SYSCALL_64_after_hwframe+0x56/0x5e

Signed-off-by: Seyediman Seyedarab <ImanDevel@...il.com>
---
 drivers/cpufreq/cpufreq.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index acf19b004..6e672dcba 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -653,10 +653,7 @@ static ssize_t store_local_boost(struct cpufreq_policy *policy,
 
 	policy->boost_enabled = enable;
 
-	cpus_read_lock();
 	ret = cpufreq_driver->set_boost(policy, enable);
-	cpus_read_unlock();
-
 	if (ret) {
 		policy->boost_enabled = !policy->boost_enabled;
 		return ret;
@@ -1045,10 +1042,12 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
 	if (!fattr->store)
 		return -EIO;
 
+	cpus_read_lock();
 	down_write(&policy->rwsem);
 	if (likely(!policy_is_inactive(policy)))
 		ret = fattr->store(policy, buf, count);
 	up_write(&policy->rwsem);
+	cpus_read_unlock();
 
 	return ret;
 }
-- 
2.49.0