* [PATCH] tracing: Fix race where histograms can be called before the event
@ 2022-11-23 21:43 Steven Rostedt
2022-11-23 23:39 ` Masami Hiramatsu
0 siblings, 1 reply; 2+ messages in thread
From: Steven Rostedt @ 2022-11-23 21:43 UTC (permalink / raw)
To: LKML, Linux Trace Kernel; +Cc: Masami Hiramatsu, Tom Zanussi
From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
commit 94eedf3dded5 ("tracing: Fix race where eprobes can be called before
the event") fixed an issue where if an event is soft disabled, and the
trigger is being added, there's a small window where the event sees that
there's a trigger but does not see that it requires reading the event yet,
and then calls the trigger with the record == NULL.
This could be solved with adding memory barriers in the hot path, or to
make sure that all the triggers requiring a record check for NULL. The
latter was chosen.
Commit 94eedf3dded5 set the eprobe trigger handle to check for NULL, but
the same needs to be done with histograms.
Link: https://lore.kernel.org/linux-trace-kernel/20221118211809.701d40c0f8a757b0df3c025a@kernel.org/
Cc: stable@vger.kernel.org
Fixes: 7491e2c442781 ("tracing: Add a probe that attaches to trace events")
Reported-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace_events_hist.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 087c19548049..1c82478e8dff 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5143,6 +5143,9 @@ static void event_hist_trigger(struct event_trigger_data *data,
void *key = NULL;
unsigned int i;
+ if (unlikely(!rbe))
+ return;
+
memset(compound_key, 0, hist_data->key_size);
for_each_hist_key_field(i, hist_data) {
--
2.35.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] tracing: Fix race where histograms can be called before the event
2022-11-23 21:43 [PATCH] tracing: Fix race where histograms can be called before the event Steven Rostedt
@ 2022-11-23 23:39 ` Masami Hiramatsu
0 siblings, 0 replies; 2+ messages in thread
From: Masami Hiramatsu @ 2022-11-23 23:39 UTC (permalink / raw)
To: Steven Rostedt; +Cc: LKML, Linux Trace Kernel, Masami Hiramatsu, Tom Zanussi
On Wed, 23 Nov 2022 16:43:23 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
>
> commit 94eedf3dded5 ("tracing: Fix race where eprobes can be called before
> the event") fixed an issue where if an event is soft disabled, and the
> trigger is being added, there's a small window where the event sees that
> there's a trigger but does not see that it requires reading the event yet,
> and then calls the trigger with the record == NULL.
>
> This could be solved with adding memory barriers in the hot path, or to
> make sure that all the triggers requiring a record check for NULL. The
> latter was chosen.
>
> Commit 94eedf3dded5 set the eprobe trigger handle to check for NULL, but
> the same needs to be done with histograms.
>
> Link: https://lore.kernel.org/linux-trace-kernel/20221118211809.701d40c0f8a757b0df3c025a@kernel.org/
>
> Cc: stable@vger.kernel.org
> Fixes: 7491e2c442781 ("tracing: Add a probe that attaches to trace events")
> Reported-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
I confirmed that other trigger callbacks only use the event_trigger_data,
So this looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Thank you!
> ---
> kernel/trace/trace_events_hist.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 087c19548049..1c82478e8dff 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -5143,6 +5143,9 @@ static void event_hist_trigger(struct event_trigger_data *data,
> void *key = NULL;
> unsigned int i;
>
> + if (unlikely(!rbe))
> + return;
> +
> memset(compound_key, 0, hist_data->key_size);
>
> for_each_hist_key_field(i, hist_data) {
> --
> 2.35.1
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
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