[PATCH 5.15 086/120] tracing: Fix race where histograms can be called before the event

Greg Kroah-Hartman
2022-12-05T19:39:38Z

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit ef38c79a522b660f7f71d45dad2d6244bc741841 upstream.

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/
Link: https://lore.kernel.org/linux-trace-kernel/20221123164323.03450c3a@gandalf.local.home

Cc: Tom Zanussi <zanussi@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>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/trace_events_hist.c | 3 +++
1 file changed, 3 insertions(+)

--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -4677,6 +4677,9 @@ static void event_hist_trigger(struct ev
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) {