v4.19.13 snapshot.
diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
new file mode 100644
index 0000000..d953c16
--- /dev/null
+++ b/kernel/trace/trace_kdb.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * kdb helper for dumping the ftrace buffer
+ *
+ * Copyright (C) 2010 Jason Wessel <jason.wessel@windriver.com>
+ *
+ * ftrace_dump_buf based on ftrace_dump:
+ * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
+ * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
+ *
+ */
+#include <linux/init.h>
+#include <linux/kgdb.h>
+#include <linux/kdb.h>
+#include <linux/ftrace.h>
+
+#include "trace.h"
+#include "trace_output.h"
+
+static void ftrace_dump_buf(int skip_lines, long cpu_file)
+{
+ /* use static because iter can be a bit big for the stack */
+ static struct trace_iterator iter;
+ static struct ring_buffer_iter *buffer_iter[CONFIG_NR_CPUS];
+ struct trace_array *tr;
+ unsigned int old_userobj;
+ int cnt = 0, cpu;
+
+ trace_init_global_iter(&iter);
+ iter.buffer_iter = buffer_iter;
+ tr = iter.tr;
+
+ for_each_tracing_cpu(cpu) {
+ atomic_inc(&per_cpu_ptr(iter.trace_buffer->data, cpu)->disabled);
+ }
+
+ old_userobj = tr->trace_flags;
+
+ /* don't look at user memory in panic mode */
+ tr->trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
+
+ kdb_printf("Dumping ftrace buffer:\n");
+
+ /* reset all but tr, trace, and overruns */
+ memset(&iter.seq, 0,
+ sizeof(struct trace_iterator) -
+ offsetof(struct trace_iterator, seq));
+ iter.iter_flags |= TRACE_FILE_LAT_FMT;
+ iter.pos = -1;
+
+ if (cpu_file == RING_BUFFER_ALL_CPUS) {
+ for_each_tracing_cpu(cpu) {
+ iter.buffer_iter[cpu] =
+ ring_buffer_read_prepare(iter.trace_buffer->buffer, cpu);
+ ring_buffer_read_start(iter.buffer_iter[cpu]);
+ tracing_iter_reset(&iter, cpu);
+ }
+ } else {
+ iter.cpu_file = cpu_file;
+ iter.buffer_iter[cpu_file] =
+ ring_buffer_read_prepare(iter.trace_buffer->buffer, cpu_file);
+ ring_buffer_read_start(iter.buffer_iter[cpu_file]);
+ tracing_iter_reset(&iter, cpu_file);
+ }
+
+ while (trace_find_next_entry_inc(&iter)) {
+ if (!cnt)
+ kdb_printf("---------------------------------\n");
+ cnt++;
+
+ if (!skip_lines) {
+ print_trace_line(&iter);
+ trace_printk_seq(&iter.seq);
+ } else {
+ skip_lines--;
+ }
+
+ if (KDB_FLAG(CMD_INTERRUPT))
+ goto out;
+ }
+
+ if (!cnt)
+ kdb_printf(" (ftrace buffer empty)\n");
+ else
+ kdb_printf("---------------------------------\n");
+
+out:
+ tr->trace_flags = old_userobj;
+
+ for_each_tracing_cpu(cpu) {
+ atomic_dec(&per_cpu_ptr(iter.trace_buffer->data, cpu)->disabled);
+ }
+
+ for_each_tracing_cpu(cpu) {
+ if (iter.buffer_iter[cpu]) {
+ ring_buffer_read_finish(iter.buffer_iter[cpu]);
+ iter.buffer_iter[cpu] = NULL;
+ }
+ }
+}
+
+/*
+ * kdb_ftdump - Dump the ftrace log buffer
+ */
+static int kdb_ftdump(int argc, const char **argv)
+{
+ int skip_lines = 0;
+ long cpu_file;
+ char *cp;
+
+ if (argc > 2)
+ return KDB_ARGCOUNT;
+
+ if (argc) {
+ skip_lines = simple_strtol(argv[1], &cp, 0);
+ if (*cp)
+ skip_lines = 0;
+ }
+
+ if (argc == 2) {
+ cpu_file = simple_strtol(argv[2], &cp, 0);
+ if (*cp || cpu_file >= NR_CPUS || cpu_file < 0 ||
+ !cpu_online(cpu_file))
+ return KDB_BADINT;
+ } else {
+ cpu_file = RING_BUFFER_ALL_CPUS;
+ }
+
+ kdb_trap_printk++;
+ ftrace_dump_buf(skip_lines, cpu_file);
+ kdb_trap_printk--;
+
+ return 0;
+}
+
+static __init int kdb_ftrace_register(void)
+{
+ kdb_register_flags("ftdump", kdb_ftdump, "[skip_#lines] [cpu]",
+ "Dump ftrace log", 0, KDB_ENABLE_ALWAYS_SAFE);
+ return 0;
+}
+
+late_initcall(kdb_ftrace_register);