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b=B6B+F/DHWL2q7ZgB0jFEn23Sxe386Z2wy7w+NbGkRfP62V4/VsAf+eeAetxsBowtdp9qEUUdGUbZb47yaC2ttJRDW3+XcZV9tmZ/CaQZcughaWQ9eXEI/50rRnE2a+rcvwFCo/VTgNjuSTva+WnwTEI5dDSCJ72u186oSMfK5qA= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DS4PR12MB999075.namprd12.prod.outlook.com (2603:10b6:8:2fc::20) by SA3PR12MB8804.namprd12.prod.outlook.com (2603:10b6:806:31f::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.292.25; Tue, 11 Aug 2026 10:54:22 +0000 Received: from DS4PR12MB999075.namprd12.prod.outlook.com ([fe80::4c9d:851d:3f44:800f]) by DS4PR12MB999075.namprd12.prod.outlook.com ([fe80::4c9d:851d:3f44:800f%6]) with mapi id 15.21.0292.024; Tue, 11 Aug 2026 10:54:22 +0000 Message-ID: <7e2a3899-b44b-4c04-af6d-b4299938f76e@amd.com> Date: Tue, 11 Aug 2026 16:24:14 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3 2/6] PM: runtime: Add pm_runtime_if_active guard and conditional variant To: sashiko-reviews@lists.linux.dev Cc: devicetree@vger.kernel.org, dmaengine@vger.kernel.org, robh@kernel.org, vkoul@kernel.org, Frank.Li@kernel.org, conor+dt@kernel.org References: <20260810100452.426320-1-nagendra.golla@amd.com> <20260810100452.426320-3-nagendra.golla@amd.com> <20260810102501.9F8321F000E9@smtp.kernel.org> Content-Language: en-US From: "Golla, Nagendra" In-Reply-To: <20260810102501.9F8321F000E9@smtp.kernel.org> Content-Type: text/plain; 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Sashiko AI review found 2 potential issue(s) to consider: > - [High] The `pm_runtime_if_active_try` guard evaluates to an error when runtime PM is disabled, violating the API contract and breaking IRQ handlers. > - [Medium] The conditionally defined base guard `guard(pm_runtime_if_active)` silently corrupts the runtime PM usage counter if used directly. > -- > > --- Patch [2]: [PATCH V3 2/6] PM: runtime: Add pm_runtime_if_active guard and conditional variant --- > commit 57173006d8cc8596d1863023936dfd41e4325af1 > Author: Golla Nagendra > > PM: runtime: Add pm_runtime_if_active guard and conditional variant > > Add a pm_runtime_if_active base guard and its _try conditional variant > to pm_runtime.h for drivers that need to conditionally acquire a runtime > PM reference only when the device is already active. > >> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h >> --- a/include/linux/pm_runtime.h >> +++ b/include/linux/pm_runtime.h >> @@ -609,6 +609,13 @@ DEFINE_GUARD(pm_runtime_active, struct device *, >> pm_runtime_get_sync(_T), pm_runtime_put(_T)); >> DEFINE_GUARD(pm_runtime_active_auto, struct device *, >> pm_runtime_get_sync(_T), pm_runtime_put_autosuspend(_T)); >> +/* >> + * Do not use directly -- the destructor calls pm_runtime_put() >> + * unconditionally, which underflows if no reference was acquired. >> + * Use only via the _try variant below. >> + */ >> +DEFINE_GUARD(pm_runtime_if_active, struct device *, >> + pm_runtime_get_if_active(_T), pm_runtime_put(_T)); > > [Severity: Medium] > While the comment warns against direct usage, does exposing this base > guard via DEFINE_GUARD in include/linux/pm_runtime.h create a risky API > footgun? > > If a developer uses guard(pm_runtime_if_active)(&dev) directly and the > device is not active, pm_runtime_get_if_active() returns 0 without > incrementing the usage counter. At scope exit, the destructor > unconditionally calls pm_runtime_put(), which would underflow the usage > counter and could prevent the device from suspending. > > Could a lock-tracking guard like DEFINE_LOCK_GUARD_1 be used instead to > avoid defining an unsafe base guard? > >> /* >> * Use the following guards with ACQUIRE()/ACQUIRE_ERR(). >> * >> @@ -624,6 +631,8 @@ DEFINE_GUARD_COND(pm_runtime_active_auto, _try, >> pm_runtime_get_active(_T, RPM_TRANSPARENT), _RET == 0) >> DEFINE_GUARD_COND(pm_runtime_active_auto, _try_enabled, >> pm_runtime_resume_and_get(_T), _RET == 0) >> +DEFINE_GUARD_COND(pm_runtime_if_active, _try, >> + pm_runtime_get_if_active(_T) ?: -EAGAIN, _RET == 1) > > [Severity: High] > Does this strict condition break interrupt handlers when runtime PM is > disabled? > > If CONFIG_PM is disabled (or runtime PM is not enabled for the device), > pm_runtime_get_if_active() returns -EINVAL. With the _RET == 1 check > in DEFINE_GUARD_COND, the guard condition fails and evaluates to > ERR_PTR(-EINVAL). > > If a driver uses PM_RUNTIME_ACQUIRE_IF_ACTIVE() in an interrupt handler > on such a system, the handler will bail out instead of servicing the valid > interrupt. This can lead to an unhandled IRQ storm that permanently > disables the device's interrupt line. > > The documented API contract for _try guards states they do not produce > an error when runtime PM is disabled. Should this handle the -EINVAL > case to safely bypass the guard when PM is disabled? Thanks for catching this Will address this in the next version. Thanks, Nagendra >