linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
* Re: [PATCH v2] tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation
@ 2020-04-14  7:54 Markus Elfring
  2020-04-15  1:40 ` Xiao Yang
  0 siblings, 1 reply; 6+ messages in thread
From: Markus Elfring @ 2020-04-14  7:54 UTC (permalink / raw)
  To: Xiao Yang, linux-kselftest, linux-trace-devel
  Cc: linux-kernel, Ingo Molnar, Steven Rostedt, Xiao Yang

> Traced event can trigger 'snapshot' operation(i.e. calls snapshot_trigger()

I suggest to improve the change description.

* Adjustment:
  … operation (i. e. …

* Will the tag “Fixes” become relevant?

Regards,
Markus

^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH v2] tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation
@ 2020-04-14  1:51 Xiao Yang
  0 siblings, 0 replies; 6+ messages in thread
From: Xiao Yang @ 2020-04-14  1:51 UTC (permalink / raw)
  To: rostedt
  Cc: mingo, linux-kernel, linux-kselftest, linux-trace-devel,
	ice_yangxiao, Xiao Yang

Traced event can trigger 'snapshot' operation(i.e. calls snapshot_trigger()
or snapshot_count_trigger()) when register_snapshot_trigger() has completed
registration but doesn't allocate buffer for 'snapshot' event trigger.  In
the rare case, 'snapshot' operation always detects the lack of allocated
buffer so make register_snapshot_trigger() allocate buffer first.

trigger-snapshot.tc in kselftest reproduces the issue on slow vm:
-----------------------------------------------------------
cat trace
...
ftracetest-3028  [002] ....   236.784290: sched_process_fork: comm=ftracetest pid=3028 child_comm=ftracetest child_pid=3036
     <...>-2875  [003] ....   240.460335: tracing_snapshot_instance_cond: *** SNAPSHOT NOT ALLOCATED ***
     <...>-2875  [003] ....   240.460338: tracing_snapshot_instance_cond: *** stopping trace here!   ***
-----------------------------------------------------------

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
---
 kernel/trace/trace_events_trigger.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index dd34a1b46a86..3a74736da363 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1088,14 +1088,10 @@ register_snapshot_trigger(char *glob, struct event_trigger_ops *ops,
 			  struct event_trigger_data *data,
 			  struct trace_event_file *file)
 {
-	int ret = register_trigger(glob, ops, data, file);
-
-	if (ret > 0 && tracing_alloc_snapshot_instance(file->tr) != 0) {
-		unregister_trigger(glob, ops, data, file);
-		ret = 0;
-	}
+	if (tracing_alloc_snapshot_instance(file->tr) != 0)
+		return 0;
 
-	return ret;
+	return register_trigger(glob, ops, data, file);
 }
 
 static int
-- 
2.25.1




^ permalink raw reply related	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-04-15  7:13 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-04-14  7:54 [PATCH v2] tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation Markus Elfring
2020-04-15  1:40 ` Xiao Yang
2020-04-15  1:46   ` Steven Rostedt
2020-04-15  1:59     ` Xiao Yang
2020-04-15  7:12     ` [v2] " Markus Elfring
  -- strict thread matches above, loose matches on Subject: below --
2020-04-14  1:51 [PATCH v2] " Xiao Yang

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).