| From f147554190678773159b1fd101887d0b39ec6d89 Mon Sep 17 00:00:00 2001 |
| From: Xiao Yang <yangx.jy@cn.fujitsu.com> |
| Date: Tue, 14 Apr 2020 09:51:45 +0800 |
| Subject: [PATCH] tracing: Fix the race between registering 'snapshot' event |
| trigger and triggering 'snapshot' operation |
| |
| commit 0bbe7f719985efd9adb3454679ecef0984cb6800 upstream. |
| |
| 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! *** |
| ----------------------------------------------------------- |
| |
| Link: http://lkml.kernel.org/r/20200414015145.66236-1-yangx.jy@cn.fujitsu.com |
| |
| Cc: stable@vger.kernel.org |
| Fixes: 93e31ffbf417a ("tracing: Add 'snapshot' event trigger command") |
| Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com> |
| Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c |
| index cd285fb612ae..39f8b3856c3a 100644 |
| --- a/kernel/trace/trace_events_trigger.c |
| +++ b/kernel/trace/trace_events_trigger.c |
| @@ -1076,14 +1076,10 @@ 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 |
| -- |
| 2.7.4 |
| |