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SubjectRe: [PATCH v3 1/2] tracing: Avoid adding tracer option before update_tracer_options
On Wed, 23 Mar 2022 23:22:56 +0800
Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote:

> 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.

> ---
> 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.

-- Steve


> mutex_unlock(&trace_types_lock);
> }
>

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