On Wed, 05 Apr 2023 09:58:15 -0400 Steven Rostedt rostedt@goodmis.org wrote:

From: "Steven Rostedt (Google)" rostedt@goodmis.org

The kernel command line ftrace_boot_snapshot by itself is supposed to trigger a snapshot at the end of boot up of the main top level trace buffer. A ftrace_boot_snapshot=foo will do the same for an instance called foo that was created by trace_instance=foo,...

The logic was broken where if ftrace_boot_snapshot was by itself, it would trigger a snapshot for all instances that had tracing enabled, regardless if it asked for a snapshot or not.

When a snapshot is requested for a buffer, the buffer's tr->allocated_snapshot is set to true. Use that to know if a trace buffer wants a snapshot at boot up or not.

Since the top level buffer is part of the ftrace_trace_arrays list, there's no reason to treat it differently than the other buffers. Just iterate the list if ftrace_boot_snapshot was specified.

Link: https://lkml.kernel.org/r/20230405022341.895334039@goodmis.org

Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Ross Zwisler zwisler@google.com Fixes: 9c1c251d670bc ("tracing: Allow boot instances to have snapshot buffers")

I guess I didn't need to Cc stable here, as the commit it fixed was added in the 6.3 merge window.

$ git describe --contains 9c1c251d670bc v6.3-rc1~126^2~8

Oh well.

-- Steve

Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org

kernel/trace/trace.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ed1d1093f5e9..4686473b8497 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -10393,19 +10393,20 @@ __init static int tracer_alloc_buffers(void) void __init ftrace_boot_snapshot(void) { +#ifdef CONFIG_TRACER_MAX_TRACE struct trace_array *tr;

• if (snapshot_at_boot) {

• tracing_snapshot();
  

• internal_trace_puts("** Boot snapshot taken **\n");
  

• }

• if (!snapshot_at_boot)

• return;
  

list_for_each_entry(tr, &ftrace_trace_arrays, list) {

• if (tr == &global_trace)
  

• if (!tr->allocated_snapshot)
  continue;
  

• trace_array_puts(tr, "** Boot snapshot taken **\n");
  

• tracing_snapshot_instance(tr);

• trace_array_puts(tr, "** Boot snapshot taken **\n");
  

  }

+#endif } void __init early_trace_init(void)