From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7B2FC18A6B0; Mon, 4 Aug 2025 00:28:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754267334; cv=none; b=mwggQzxpQjncNd8lY/eJaaWnv6ouVB3QQ9J4vXiCoaC/ds1aQsviu7LWgDkNp7iunwTeq0LnF3x+D/G4kYYzMm8eSmX4xaoFP6LA3hEdR986jy7Zp7D2qNK5e/P1gbOxKG/8FDdY1UG5oQVIAl8PM44ClOQYvJhOtONdPCt0STE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754267334; c=relaxed/simple; bh=7mN0nWGnCYOCncbmMteAajT4rE7Vt/r1IlxvI28H+kM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Wpr/RLpt0tOG09YucdFHcGBx7J9ciP1Vus/ke1XPbcumvRn5Z4k0RNoScv49sKfFVSpfoW1MFBr+b5DotulsikI7iGtYWnovlvoH4QZ6DPVezvk9Rwl1nIf7pKW78YNekWhuRMwgUsmcfokUfsrGQanAqHx57FjdmFPMoGTmRJ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=n5x3D7zK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="n5x3D7zK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0425CC4CEF8; Mon, 4 Aug 2025 00:28:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754267334; bh=7mN0nWGnCYOCncbmMteAajT4rE7Vt/r1IlxvI28H+kM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n5x3D7zKS3qVRtV1PMIt6zVmSZP5xz0OLyl8+fDkllVmGSbxyJi2pCm9p+nHlTT/0 oRj0Ikf67LCyYVAXcko2EFWGONNTAdY6FaVg8FEDY/qcRIy7HA0r1X22Ki+WR3+aV+ XnLQSk6tiR8L1Sy0+AKyoWSPTLsYKTv8OUuLW2Fg5beK21BOw4du7pI29+iqpupwUF mHE8fKiBxjXAuh7c772ICDm5VMkf9LwCfiwdHYo7xIJ6Vk0NVl1AhI4PAVKyMgN+Si D9R2snOSD31UrinQxp1/hENC4eAb9ktSbDxYTKj8zPLuLB8g/si3R+m0X1euE8dW+3 0eLoJKpQL5Xaw== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Lifeng Zheng , "Rafael J . Wysocki" , Sasha Levin , rafael@kernel.org, viresh.kumar@linaro.org, linux-pm@vger.kernel.org Subject: [PATCH AUTOSEL 6.15 23/80] cpufreq: Exit governor when failed to start old governor Date: Sun, 3 Aug 2025 20:26:50 -0400 Message-Id: <20250804002747.3617039-23-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250804002747.3617039-1-sashal@kernel.org> References: <20250804002747.3617039-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.15.9 Content-Transfer-Encoding: 8bit From: Lifeng Zheng [ Upstream commit 0ae204405095abfbc2d694ee0fbb49bcbbe55c57 ] Detect the result of starting old governor in cpufreq_set_policy(). If it fails, exit the governor and clear policy->governor. Signed-off-by: Lifeng Zheng Link: https://patch.msgid.link/20250709104145.2348017-5-zhenglifeng1@huawei.com Signed-off-by: Rafael J. Wysocki Signed-off-by: Sasha Levin --- LLM Generated explanations, may be completely bogus: **Backport Status: YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Bug Analysis The commit fixes a **resource leak and inconsistent state bug** in the cpufreq governor switching code. Looking at the code changes in `cpufreq_set_policy()`: ### The Bug: In the original code (lines 2716-2721), when switching governors fails and we need to restore the old governor: ```c if (old_gov) { policy->governor = old_gov; if (cpufreq_init_governor(policy)) policy->governor = NULL; else cpufreq_start_governor(policy); // Bug: no error handling here } ``` If `cpufreq_start_governor()` fails, the code doesn't handle the error. This leaves the system in an **inconsistent state** where: 1. The governor is initialized (`cpufreq_init_governor` succeeded) 2. But the governor failed to start (`cpufreq_start_governor` failed) 3. The policy still points to a non-functional governor 4. Resources allocated during `cpufreq_init_governor` are **leaked** (module reference count, governor's init() allocations) ### The Fix: ```c if (cpufreq_init_governor(policy)) { policy->governor = NULL; } else if (cpufreq_start_governor(policy)) { cpufreq_exit_governor(policy); // NEW: Clean up on failure policy->governor = NULL; // NEW: Clear the governor pointer } ``` ## Why This Should Be Backported: 1. **Fixes a Real Bug**: This addresses a resource leak where `cpufreq_init_governor()` acquires resources (notably `try_module_get()` at line 2442 and potential governor->init() allocations) that aren't cleaned up if `cpufreq_start_governor()` fails. 2. **Small and Contained Fix**: The change is minimal - just 4 lines modified to add proper error handling. It doesn't change any APIs or introduce new functionality. 3. **Prevents System Instability**: Leaving the cpufreq subsystem in an inconsistent state (initialized but not started governor) could lead to: - Module reference count leaks - Memory leaks from governor init allocations - Potential crashes if the partially-initialized governor is accessed later 4. **Error Path Fix**: This is clearly an error handling path that was incorrectly implemented. The pattern of calling `cpufreq_exit_governor()` after a failed `cpufreq_start_governor()` is already used elsewhere in the code (line 2711). 5. **No Architectural Changes**: The fix simply adds missing cleanup code in an error path. It doesn't change the normal operation flow or introduce new features. 6. **Critical Subsystem**: The cpufreq subsystem is critical for power management and system stability. Bugs here can affect system reliability. The commit follows the stable kernel rules perfectly - it's a clear bug fix that prevents resource leaks and system instability, with minimal risk of regression since it only affects an error path that was already broken. drivers/cpufreq/cpufreq.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index f45ded62b0e0..32ed5bc15147 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -2784,10 +2784,12 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, pr_debug("starting governor %s failed\n", policy->governor->name); if (old_gov) { policy->governor = old_gov; - if (cpufreq_init_governor(policy)) + if (cpufreq_init_governor(policy)) { policy->governor = NULL; - else - cpufreq_start_governor(policy); + } else if (cpufreq_start_governor(policy)) { + cpufreq_exit_governor(policy); + policy->governor = NULL; + } } return ret; -- 2.39.5