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Mon, 28 Sep 2020 12:42:09 +0000 Subject: Re: [PATCH] time/sched_clock: mark sched_clock_read_begin as notrace To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Leo Yan , Will Deacon , a.darwish@linutronix.de, Daniel Lezcano , Paul Cercueil , Randy Dunlap , ben.dooks@codethink.co.uk, Steven Rostedt References: <20200928104952.26892-1-quanyang.wang@windriver.com> <20200928105859.GF2628@hirez.programming.kicks-ass.net> From: Quanyang Wang Message-ID: <22a5d255-7a9f-3139-1e8a-4263fea690c0@windriver.com> Date: Mon, 28 Sep 2020 20:41:59 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <20200928105859.GF2628@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-ClientProxiedBy: HK2PR04CA0047.apcprd04.prod.outlook.com (2603:1096:202:14::15) To CY4PR11MB0071.namprd11.prod.outlook.com (2603:10b6:910:7a::30) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [128.224.162.199] (60.247.85.82) by HK2PR04CA0047.apcprd04.prod.outlook.com (2603:1096:202:14::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3412.22 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-OriginatorOrg: windriver.com X-MS-Exchange-CrossTenant-Network-Message-Id: fdac5aa7-dba2-45d4-b248-08d863abea06 X-MS-Exchange-CrossTenant-AuthSource: CY4PR11MB0071.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Sep 2020 12:42:09.2518 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ddb2873-a1ad-4a18-ae4e-4644631433be X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: J491FmWsee4xmHY/8NcVCgSo/lDkQ66RO6lfm/A7k5A/equLe4OM8wj5ThPpEEqx5cNmvc8D77rMKgqKcCuFa7MyVy9oFHNz9kwXJYaQJwo= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR11MB1941 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On 9/28/20 6:58 PM, Peter Zijlstra wrote: > On Mon, Sep 28, 2020 at 06:49:52PM +0800, quanyang.wang@windriver.com wrote: >> From: Quanyang Wang >> >> Since sched_clock_read_begin is called by notrace function sched_clock, >> it shouldn't be traceable either, or else __ftrace_graph_caller will >> run into a dead loop on the path (arm for instance): >> >> ftrace_graph_caller >> prepare_ftrace_return >> function_graph_enter >> ftrace_push_return_trace >> trace_clock_local >> sched_clock >> sched_clock_read_begin >> >> Fixes: 1b86abc1c645 ("sched_clock: Expose struct clock_read_data") >> Signed-off-by: Quanyang Wang >> --- >> kernel/time/sched_clock.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c >> index 1c03eec6ca9b..58459e1359d7 100644 >> --- a/kernel/time/sched_clock.c >> +++ b/kernel/time/sched_clock.c >> @@ -68,7 +68,7 @@ static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift) >> return (cyc * mult) >> shift; >> } >> >> -struct clock_read_data *sched_clock_read_begin(unsigned int *seq) >> +notrace struct clock_read_data *sched_clock_read_begin(unsigned int *seq) >> { >> *seq = raw_read_seqcount_latch(&cd.seq); >> return cd.read_data + (*seq & 1); > At the very least sched_clock_read_retry() should also be marked such. In fact, the sched_clock_read_retry is treated as a "inline" function, so it doesn't trigger the  dead loop. But for safe, add notrace to it is better. I will send a V2 patch. Thanks, Quanyang > > But Steve, how come x86 works? Our sched_clock() doesn't have notrace on > at all.