2020-09-29 02:16:01

by quanyang wang

Subject: [PATCH V2] time/sched_clock: mark sched_clock_read_begin/retry as notrace

From: Quanyang Wang <[email protected]>

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 <[email protected]>
---
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);
}
--
2.17.1

2020-09-29 07:53:15

by Peter Zijlstra

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, [email protected] wrote:
> From: Quanyang Wang <[email protected]>
>
> 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 <[email protected]>
> ---
> 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) <[email protected]>

2020-09-29 08:11:17

by quanyang wang

Subject: Re: [PATCH V2] time/sched_clock: mark sched_clock_read_begin/retry as notrace

Hi Peter,

On 9/29/20 3:49 PM, Peter Zijlstra wrote:
> On Tue, Sep 29, 2020 at 09:50:51AM +0800, [email protected] wrote:
>> From: Quanyang Wang <[email protected]>
>>
>> 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 <[email protected]>
>> ---
>> 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.

Thanks for your review. I will send a V3 patch to fix it.

Thanks,

Quanyang

>
> In any case,
>
> Acked-by: Peter Zijlstra (Intel) <[email protected]>