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SubjectRe: [PATCH v3 1/2] tracing: Avoid adding tracer option before update_tracer_options
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> > To prepare for support asynchronous tracer_init_tracefs initcall,
> > avoid calling create_trace_option_files before __update_tracer_options.
> > Otherwise, create_trace_option_files will show warning because
> > some tracers in trace_types list are already in tr->topts.
> >
> > For example, hwlat_tracer call register_tracer in late_initcall,
> > and global_trace.dir is already created in tracing_init_dentry,
> > hwlat_tracer will be put into tr->topts.
> > Then if the __update_tracer_options is executed after hwlat_tracer
> > registered, create_trace_option_files find that hwlat_tracer is
> > already in tr->topts.
> >
> > 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>
>
> Before this patch:
>
> # ls /sys/kernel/tracing/options
> annotate funcgraph-duration hex stacktrace
> bin funcgraph-irqs irq-info sym-addr
> blk_cgname funcgraph-overhead latency-format sym-offset
> blk_cgroup funcgraph-overrun markers sym-userobj
> blk_classic funcgraph-proc overwrite test_nop_accept
> block funcgraph-tail pause-on-trace test_nop_refuse
> context-info func-no-repeats printk-msg-only trace_printk
> disable_on_free func_stack_trace print-parent userstacktrace
> display-graph function-fork raw verbose
> event-fork function-trace record-cmd
> funcgraph-abstime graph-time record-tgid
> funcgraph-cpu hash-ptr sleep-time
>
>
> After this patch:
>
> # ls /sys/kernel/tracing/options
> annotate disable_on_free irq-info raw trace_printk
> bin display-graph latency-format record-cmd userstacktrace
> blk_cgname event-fork markers record-tgid verbose
> blk_cgroup function-fork overwrite stacktrace
> blk_classic function-trace pause-on-trace sym-addr
> block hash-ptr printk-msg-only sym-offset
> context-info hex print-parent sym-userobj
>
> Not good.

Calling __update_tracer_options() when tracer_options_updated=false have no
effect because it return directly in add_tracer_options().
I will fix it in v4 as you suggest in the below comment.

>
> > ---
> > kernel/trace/trace.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index eb44418574f9..85ec758c4455 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);
> > __update_tracer_options(tr);
> > + tracer_options_updated = true;
>
> I think you want to set this before the __update, as doing it after just
> makes the update a nop.

You are right.
I will update in v4, thanks!

>
> -- Steve
>
>
> > mutex_unlock(&trace_types_lock);
> > }
> >

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