From cca990c7b565af0dc61a8f647c00833453cf5bff Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Google)" Date: Thu, 22 Feb 2024 20:33:24 -0500 Subject: [PATCH] tracing: Fix snapshot counter going between two tracers that use it 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 tracer that uses the snapshot is enabled even if the snapshot was used by the previous tracer. That is: # cd /sys/kernel/tracing # echo wakeup_rt > current_tracer # echo wakeup_dl > current_tracer # echo nop > current_tracer would leave the snapshot counter at 1 and not zero. That's because the enabling of wakeup_dl would increment the counter again but the setting the tracer to nop would only decrement it once. Do not arm the snapshot for a tracer if the previous tracer already had it armed. Link: https://lore.kernel.org/linux-trace-kernel/20240223013344.570525723@goodmis.org Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Cc: Vincent Donnefort Fixes: 16f7e48ffc53a ("tracing: Add snapshot refcount") Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index a7c0dc0aaf14..1e1fd377a1cf 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6162,7 +6162,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf) tracing_disarm_snapshot(tr); } - if (t->use_max_tr) { + if (!had_max_tr && t->use_max_tr) { ret = tracing_arm_snapshot_locked(tr); if (ret) goto out; -- 2.39.5