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 9E4981519A0; Mon, 4 Aug 2025 00:42:46 +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=1754268166; cv=none; b=ZPV+t1eGo1nivZK8i9RLLah4kdhoryxzLV4qkqN3MBeK9Gve6aqw/D8IbpkV56GhX6Yjoj5v9+Sk3VQijipQ+btIEsnRax1/wMApmxIAHuSoTjXfxOdZWIBCf3LLB0OWkSr6Z7UF4fUJsofXR3iy17tczt4uHR74ri9XD0wuSEw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754268166; c=relaxed/simple; bh=dljcmrZyQ6cYAqyndDCAPMnqOk7KaindJMW7AjvhsCY=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=QRKxjN5+Ym8TZQQbeWfn7c565t5M64W/VtFDd1MhA9gIn/eWJNjDa+sJmLJPLpNvr/AbvbrDuXiEPVHfcGi6G9hKlfzZ/Ulss4nU1FmvM+c0XPwPDK6oovBaFPKzOg3r/mJtZxWNi3fNm4WmxgVCujbQgjNFHkwndaJ5BZ02F1o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=n3DFI8wk; 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="n3DFI8wk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 26AB6C4CEF0; Mon, 4 Aug 2025 00:42:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754268166; bh=dljcmrZyQ6cYAqyndDCAPMnqOk7KaindJMW7AjvhsCY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n3DFI8wkLpAN9t0hhcLOtM0LtvjY1C3idybm1mkVBBmMtwssCN94M4tYEky3Ti5mO zBk2bj+1STZhVbpmxToYT5ic0QPRoOPM+b+LyAfFJ7LBLqA/e6h5QR05uEG6FOKnAV XA0AB4CKKwb17oSl1IqR4Ewa45d6/u7M4T8ZpA8PKxbSjy27n3vwWaPzmbAg7cpsU6 7tFB7TtmZ6wQOtB49mzaRj1V/fKGMbgdWswzQSyKKYO8aKHcj9vPM6EFeSI6Td+hGi g5tQc474EzbcSqpRJrFbWRvvyfEiqg8q1slxF0AkWVxmj3jgI/X0ncdtAvw5sWvZdT 62wmWkhzg24bw== 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 5.4 08/28] cpufreq: Exit governor when failed to start old governor Date: Sun, 3 Aug 2025 20:42:07 -0400 Message-Id: <20250804004227.3630243-8-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250804004227.3630243-1-sashal@kernel.org> References: <20250804004227.3630243-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.4.296 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 2a2fea6743aa..0bb17bb615f5 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -2482,10 +2482,12 @@ 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