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Mon, 12 May 2025 18:54:59 -0700 (PDT) Received: from iman-pc.home ([142.186.8.171]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6f6e3a47311sm60064036d6.73.2025.05.12.18.54.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 May 2025 18:54:58 -0700 (PDT) From: Seyediman Seyedarab X-Google-Original-From: Seyediman Seyedarab To: rafael@kernel.org, viresh.kumar@linaro.org Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, linux-kernel-mentees@lists.linux.dev, Seyediman Seyedarab Subject: [PATCH] cpufreq: drop redundant cpus_read_lock() from store_local_boost() Date: Mon, 12 May 2025 21:57:26 -0400 Message-ID: <20250513015726.1497-1-ImanDevel@gmail.com> X-Mailer: git-send-email 2.49.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D 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+0x5= 6/0xd0 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 --- 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; =20 - cpus_read_lock(); ret =3D policy_set_boost(policy, enable); - cpus_read_unlock(); - if (!ret) return count; =20 --=20 2.49.0