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SubjectRe: [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@windriver.com wrote:
> From: Quanyang Wang <quanyang.wang@windriver.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@windriver.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@infradead.org>

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