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dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=none action=none header.from=windriver.com; Received: from DM8PR11MB5734.namprd11.prod.outlook.com (2603:10b6:8:31::22) by DM6PR11MB4201.namprd11.prod.outlook.com (2603:10b6:5:200::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4287.22; Mon, 5 Jul 2021 14:52:42 +0000 Received: from DM8PR11MB5734.namprd11.prod.outlook.com ([fe80::bce8:81f7:f5a1:af19]) by DM8PR11MB5734.namprd11.prod.outlook.com ([fe80::bce8:81f7:f5a1:af19%6]) with mapi id 15.20.4287.033; Mon, 5 Jul 2021 14:52:42 +0000 Subject: Re: [RFC][PATCH 1/4] locking/mutex: Use try_cmpxchg() To: Peter Zijlstra Cc: mingo@redhat.com, longman@redhat.com, boqun.feng@gmail.com, will@kernel.org, linux-kernel@vger.kernel.org References: <20210630153516.832731403@infradead.org> <20210630154114.834438545@infradead.org> From: "Xu, Yanfei" Message-ID: <320cf54f-719c-8aa5-17af-455a53db4478@windriver.com> Date: Mon, 5 Jul 2021 22:52:34 +0800 User-Agent: Mozilla/5.0 (X11; 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Should we consider the race condition as blow? >> >> From 4035f50c96e17cbe3febab768b64da5c000e5b76 Mon Sep 17 00:00:00 2001 >> From: Yanfei Xu >> Date: Mon, 5 Jul 2021 17:56:58 +0800 >> Subject: [PATCH] locking/mutex: fix the endless loop when racing against >> mutex.owner >> >> if a race condition happened on mutex.owner after we fetch its value, >> atomic_long_try_cmpxchg_acquire/release invoked on &mutex.owner will >> return false. Then we need to reassign the temporary variable which >> saves mutex.owner value if in loop, or it will lead an endless loop. > > No, when try_cmpxchg() fails it will update oldp. This is the reason old > is now a pointer too. Got it. Thanks! Yanfei >