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Date: Tue, 29 Sep 2020 09:49:30 +0200 From: Peter Zijlstra <peterz@...radead.org> To: quanyang.wang@...driver.com Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Leo Yan <leo.yan@...aro.org>, Will Deacon <will@...nel.org>, a.darwish@...utronix.de, Daniel Lezcano <daniel.lezcano@...aro.org>, Paul Cercueil <paul@...pouillou.net>, Randy Dunlap <rdunlap@...radead.org>, ben.dooks@...ethink.co.uk Subject: Re: [PATCH V2] time/sched_clock: mark sched_clock_read_begin/retry as notrace On Tue, Sep 29, 2020 at 09:50:51AM +0800, quanyang.wang@...driver.com wrote: > From: Quanyang Wang <quanyang.wang@...driver.com> > > 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 <quanyang.wang@...driver.com> > --- > 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. In any case, Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
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