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Mon, 25 Nov 2024 15:35:44 +0000 Message-ID: Date: Mon, 25 Nov 2024 16:35:35 +0100 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 4/5] tracing: Remove conditional locking from __DO_TRACE() To: Peter Zijlstra , Mathieu Desnoyers CC: Linus Torvalds , Dmitry Torokhov , Steven Rostedt , , Thomas Gleixner , "Michael Jeanson" , Masami Hiramatsu , Alexei Starovoitov , Yonghong Song , "Paul E . McKenney" , Ingo Molnar , "Arnaldo Carvalho de Melo" , Mark Rutland , Alexander Shishkin , Namhyung Kim , Andrii Nakryiko , , Joel Fernandes , Jordan Rife , References: <20241123153031.2884933-1-mathieu.desnoyers@efficios.com> <20241123153031.2884933-5-mathieu.desnoyers@efficios.com> <20241125142606.GG38837@noisy.programming.kicks-ass.net> From: Przemek Kitszel Content-Language: en-US In-Reply-To: <20241125142606.GG38837@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MI0P293CA0015.ITAP293.PROD.OUTLOOK.COM (2603:10a6:290:44::8) To MN6PR11MB8102.namprd11.prod.outlook.com (2603:10b6:208:46d::9) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN6PR11MB8102:EE_|PH0PR11MB7633:EE_ X-MS-Office365-Filtering-Correlation-Id: ee4fa613-e85d-497b-4258-08dd0d66d333 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016; 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I suspect >> this is something worth discussing: >> >> static inline void trace_##name(proto) \ >> { \ >> if (static_branch_unlikely(&__tracepoint_##name.key)) { \ >> if (cond) \ >> scoped_guard(preempt_notrace) \ >> __DO_TRACE_CALL(name, TP_ARGS(args)); \ > > So coding style would like braces here for it being multi-line. As > opposed to C that only mandates it for multi-statement. And then the > problem doesn't occur. > >> } \ >> if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \ >> WARN_ONCE(!rcu_is_watching(), \ >> "RCU not watching for tracepoint"); \ >> } \ >> } >> > >> I suspect this is caused by the "else" at the end of the __scoped_guard() macro: >> >> #define __scoped_guard(_name, _label, args...) \ >> for (CLASS(_name, scope)(args); \ >> __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name); \ >> ({ goto _label; })) \ >> if (0) { \ >> _label: \ >> break; \ >> } else >> >> #define scoped_guard(_name, args...) \ >> __scoped_guard(_name, __UNIQUE_ID(label), args) >> >> AFAIU this is a new warning introduced by >> >> commit fcc22ac5baf ("cleanup: Adjust scoped_guard() macros to avoid potential warning") > > Yeah,.. So strictly speaking the code is fine, but the various compilers > don't like it when that else dangles :/ At one point I had a version that did: if (0) label: ; else for (....) but it is goto-jumping back in the code https://lore.kernel.org/netdev/20241001145718.8962-1-przemyslaw.kitszel@intel.com/#t I could switch to it again to reduce noise like this problem, but such change would be to essentially allow bad formatting