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authorSteven Rostedt (Google) <rostedt@goodmis.org>2024-02-22 20:33:24 -0500
committerSteven Rostedt (Google) <rostedt@goodmis.org>2024-03-18 10:33:05 -0400
commitcca990c7b565af0dc61a8f647c00833453cf5bff (patch)
tree4a0af7f7b91086e09ff48c5fe7e7790751bf673f /kernel
parent70a6ed553f7d3504febac467cb4a0bae621ba3c6 (diff)
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 <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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/trace.c2
1 files changed, 1 insertions, 1 deletions
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;