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authorXiao Yang <yangx.jy@cn.fujitsu.com>2020-04-14 09:51:45 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-04-24 07:59:06 +0200
commita289fd864722dcf5363fec66a35965d4964df515 (patch)
tree1c0c89fcfe401dc686b2c379c5d3371682f38626
parent5fadf30330d9dd4725d57cf06e7799c1f9c69edf (diff)
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/trace/trace_events_trigger.c10
1 files changed, 3 insertions, 7 deletions
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 8a88e85c8c61..c9ca2ed50c0e 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1068,14 +1068,10 @@ 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() != 0) {
- unregister_trigger(glob, ops, data, file);
- ret = 0;
- }
+ if (tracing_alloc_snapshot() != 0)
+ return 0;
- return ret;
+ return register_trigger(glob, ops, data, file);
}
static int