On 2020/4/13 23:02, Steven Rostedt wrote:
On Mon, 13 Apr 2020 15:12:52 +0800 Xiao Yangyangx.jy@cn.fujitsu.com wrote:
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 spare buffer for 'snapshot' event trigger. 'snapshot' operation always detects the lack of allocated buffer in the rare case so make register_snapshot_trigger() allocate spare 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 Yangyangx.jy@cn.fujitsu.com
kernel/trace/trace_events_trigger.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c index dd34a1b46a86..00e54cdcef3e 100644 --- a/kernel/trace/trace_events_trigger.c +++ b/kernel/trace/trace_events_trigger.c @@ -1088,9 +1088,13 @@ 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);
- int alloc_ret, ret;
- if (ret> 0&& tracing_alloc_snapshot_instance(file->tr) != 0) {
- alloc_ret = tracing_alloc_snapshot_instance(file->tr);
- ret = register_trigger(glob, ops, data, file);
- if (ret> 0&& alloc_ret != 0) { unregister_trigger(glob, ops, data, file); ret = 0; }
Why register if the allocation failed? Just switch the logic:
int ret = tracing_alloc_snapshot_instance(file->tr);
if (ret != 0) return 0;
return register_trigger(glob, ops, data, file);
Hi Steve,
It looks simpler and better. I think we can drop the unnecessary ret variable as well.
Thanks, Xiao Yang
-- Steve
.