Messages in this thread Patch in this message | | | From | Mark-PK Tsai <> | Subject | Re: [PATCH] tracing: Avoid adding duplicated tracer options when update_tracer_options is running in parallel | Date | Wed, 23 Mar 2022 22:21:29 +0800 |
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> On Wed, 23 Mar 2022 11:24:42 +0800 > Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote: > > > When update_tracer_options is running in parallel, > > tr->tops might be updated before the trace_types list traversal. > > Let update_tracer_options traverse the trace_types list safely in > > kernel init time and avoid the tr->tops update before it finish. > > ??? Have you seen a bug here? I'm totally confused by this.
Sorry to make you confused.
After the below patch, update_tracer_options might be executed later than registering hwlat_tracer, which is in late_initcall.
https://lore.kernel.org/lkml/20220316151639.9216-1-mark-pk.tsai@mediatek.com/
The init_hwlat_tracer initcall will put hwlat_tracer to tr->tops. Then when the later arrived __update_tracer_options is trying to update all the tracer options, create_trace_option_files show the below warning because hwlat_tracer is already in the list.
[ 6.680068 ][ T7 ] WARNING: CPU: 0 PID: 7 at kernel/trace/trace.c:8899 create_trace_option_files (kernel/trace/trace.c:8899 (discriminator 1))
full log: https://lore.kernel.org/lkml/20220322133339.GA32582@xsang-OptiPlex-9020/
> > > > > Link: https://lore.kernel.org/lkml/20220322133339.GA32582@xsang-OptiPlex-9020/ > > Reported-by: kernel test robot <oliver.sang@intel.com> > > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com> > > --- > > kernel/trace/trace.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > > index adb37e437a05..2974ae056068 100644 > > --- a/kernel/trace/trace.c > > +++ b/kernel/trace/trace.c > > @@ -6317,12 +6317,18 @@ static void tracing_set_nop(struct trace_array *tr) > > tr->current_trace = &nop_trace; > > } > > > > +static bool tracer_options_updated; > > + > > static void add_tracer_options(struct trace_array *tr, struct tracer *t) > > { > > /* Only enable if the directory has been created already. */ > > if (!tr->dir) > > return; > > > > + /* Only create trace option files after update_tracer_options finish */ > > + if (!tracer_options_updated) > > + return; > > + > > create_trace_option_files(tr, t); > > } > > > > @@ -9133,6 +9139,7 @@ static void update_tracer_options(struct trace_array *tr) > > { > > mutex_lock(&trace_types_lock); > > How is update_trace_options run in parallel? > > There's a mutex that protects it. >
Oh sorry. What I trying to tell is that update_trace_options is run in parallel with the initcall thread after:
https://lore.kernel.org/lkml/20220316151639.9216-1-mark-pk.tsai@mediatek.com/
> -- Steve > > > > __update_tracer_options(tr); > > + tracer_options_updated = true; > > mutex_unlock(&trace_types_lock); > > } > >
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