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.

Cc: stable@vger.kernel.org Fixes: 9c1c251d670bc ("tracing: Allow boot instances to have snapshot buffers") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- Changes since v1: https://lkml.kernel.org/r/20230404230308.501833715@goodmis.org

- Protect use of tr->allocated_snapshot around #ifdef TRACER_MAX_TRACE

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 93740a9370c6..36a6037823cd 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -10394,19 +10394,20 @@ __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)