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Tue, 29 Sep 2020 08:09:24 +0000 Received: from CY4PR11MB0071.namprd11.prod.outlook.com ([fe80::2d47:2e9c:cfbe:6fb2]) by CY4PR11MB0071.namprd11.prod.outlook.com ([fe80::2d47:2e9c:cfbe:6fb2%6]) with mapi id 15.20.3370.033; Tue, 29 Sep 2020 08:09:24 +0000 Subject: Re: [PATCH V2] time/sched_clock: mark sched_clock_read_begin/retry 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 References: <20200929015051.4097-1-quanyang.wang@windriver.com> <20200929074930.GG2611@hirez.programming.kicks-ass.net> From: Quanyang Wang Message-ID: <3e9755ef-cf20-b5a6-455e-a11e110e6325@windriver.com> Date: Tue, 29 Sep 2020 16:09:15 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <20200929074930.GG2611@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-ClientProxiedBy: HK2PR06CA0016.apcprd06.prod.outlook.com (2603:1096:202:2e::28) 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 HK2PR06CA0016.apcprd06.prod.outlook.com (2603:1096:202:2e::28) 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: 768b0875-bcdc-4807-c56c-08d8644efa0c X-MS-Exchange-CrossTenant-AuthSource: CY4PR11MB0071.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Sep 2020 08:09:24.4019 (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: J/zxvIo3dpWFLa2QCZClF4i7pDSzLqtm9ld2WLk25p/kQC5VwumqiJzPLzm01tttOpG2Q0V4UlQ78MrXvoyFEGY+W87kxQkFr6NXa35oNHE= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR11MB1525 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On 9/29/20 3:49 PM, Peter Zijlstra wrote: > On Tue, Sep 29, 2020 at 09:50:51AM +0800, quanyang.wang@windriver.com wrote: >> From: Quanyang Wang >> >> Since sched_clock_read_begin and sched_clock_read_retry are called >> by notrace function sched_clock, they shouldn't be traceable either, >> or else ftrace_graph_caller will run into a dead loop on the path >> as below (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/retry >> >> Fixes: 1b86abc1c645 ("sched_clock: Expose struct clock_read_data") >> Signed-off-by: Quanyang Wang >> --- >> Changes: >> V2: Add notrace to sched_clock_read_retry according to Peter's suggestion. >> >> kernel/time/sched_clock.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c >> index 1c03eec6ca9b..f629e3f5afbe 100644 >> --- a/kernel/time/sched_clock.c >> +++ b/kernel/time/sched_clock.c >> @@ -68,13 +68,13 @@ 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); >> } >> >> -int sched_clock_read_retry(unsigned int seq) >> +int notrace sched_clock_read_retry(unsigned int seq) >> { >> return read_seqcount_retry(&cd.seq, seq); >> } > You're inconsistent in the placement of notrace, I prefer the first, the > second read like notrace is the return type instead of a qualifier. Thanks for your review. I will send a V3 patch to fix it. Thanks, Quanyang > > In any case, > > Acked-by: Peter Zijlstra (Intel)