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SubjectRe: [PATCH] time/sched_clock: mark sched_clock_read_begin as notrace
On Mon, Sep 28, 2020 at 06:49:52PM +0800, quanyang.wang@windriver.com wrote:
> From: Quanyang Wang <quanyang.wang@windriver.com>
>
> 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 <quanyang.wang@windriver.com>
> ---
> 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.

But Steve, how come x86 works? Our sched_clock() doesn't have notrace on
at all.

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