[PATCH V3] time/sched_clock: mark sched_clock_read_begin/retry as notrace

[PATCH V3] time/sched_clock: mark sched_clock_read_begin/retry as notrace

[quanyang.wang]

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>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
Changes:
V2: Add notrace to sched_clock_read_retry according to Peter's suggestion.
V3: Adjust the placement of notrace 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)
+notrace int sched_clock_read_retry(unsigned int seq)
 {
 	return read_seqcount_retry(&cd.seq, seq);
 }
-- 
2.17.1

[tip: timers/urgent] time/sched_clock: Mark sched_clock_read_begin/retry() as notrace

[tip-bot2 for Quanyang Wang]

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     4cd2bb12981165f865d2b8ed92b446b52310ef74
Gitweb:        https://git.kernel.org/tip/4cd2bb12981165f865d2b8ed92b446b52310ef74
Author:        Quanyang Wang <quanyang.wang@windriver.com>
AuthorDate:    Tue, 29 Sep 2020 16:20:27 +08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 26 Oct 2020 11:34:31 +01:00

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
---
 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 0642013..b1b9b12 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)
+notrace int sched_clock_read_retry(unsigned int seq)
 {
 	return read_seqcount_latch_retry(&cd.seq, seq);
 }