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tracing: Decrement the snapshot if the snapshot trigger fails to register 

Running the ftrace selftests caused the ring buffer mapping test to fail.
Investigating, I found that the snapshot counter would be incremented
every time a snapshot trigger was added, even if that snapshot trigger
failed.

 # cd /sys/kernel/tracing
 # echo "snapshot" > events/sched/sched_process_fork/trigger
 # echo "snapshot" > events/sched/sched_process_fork/trigger
 -bash: echo: write error: File exists

That second one that fails increments the snapshot counter but doesn't
decrement it. It needs to be decremented when the snapshot fails.

Link: https://lore.kernel.org/linux-trace-kernel/20240223013344.729055907@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Fixes: 16f7e48ffc53a ("tracing: Add snapshot refcount")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Google) 2024-02-22 20:33:25 -05:00
parent cca990c7b5
commit 2048fdc275
1 changed files with 4 additions and 1 deletions
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5
kernel/trace/trace_events_trigger.c
View File

@ -1491,7 +1491,10 @@ register_snapshot_trigger(char *glob,
if (ret < 0)
return ret;
return register_trigger(glob, data, file);
ret = register_trigger(glob, data, file);
if (ret < 0)
tracing_disarm_snapshot(file->tr);
return ret;
}
static void unregister_snapshot_trigger(char *glob,