time/sched_clock: Mark sched_clock_read_begin/retry() as notrace

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200929082027.16787-1-quanyang.wang@windriver.com

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 0642013..b1b9b12 100644 (file)
--- 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;
 }
 
        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);
 }
 
 {
        *seq = raw_read_seqcount_latch(&cd.seq);
        return cd.read_data + (*seq & 1);
 }
 

-int sched_clock_read_retry(unsigned int seq)
+notrace int sched_clock_read_retry(unsigned int seq)

 {
        return read_seqcount_latch_retry(&cd.seq, seq);
 }
 {
        return read_seqcount_latch_retry(&cd.seq, seq);
 }