[PATCH 2/5] tracing: Allow trace_printk() to go to other instance buffers

Steven Rostedt
2024-08-23T01:39:46Z

Currently, trace_printk() just goes to the top level ring buffer. But
there may be times that it should go to one of the instances created by
the kernel command line.

Add a new trace_instance flag: traceprintk (also can use "printk" or
"trace_printk" as people tend to forget the actual flag name).

trace_instance=foo^traceprintk

Will assign the trace_printk to this buffer at boot up.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
.../admin-guide/kernel-parameters.txt | 14 ++++--
kernel/trace/trace.c | 46 ++++++++++++++-----
2 files changed, 45 insertions(+), 15 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3803f2b7f065..a8803c0c0a89 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6744,11 +6744,17 @@
event, and all events under the "initcall" system.

Flags can be added to the instance to modify its behavior when it is
- created. The flags are separated by '^'. Currently there's only one flag
- defined, and that's "traceoff", to have the tracing instance tracing
- disabled after it is created.
+ created. The flags are separated by '^'.

- trace_instance=foo^traceoff,sched,irq
+ The available flags are:
+
+ traceoff - Have the tracing instance tracing disabled after it is created.
+ traceprintk - Have trace_printk() write into this trace instance
+ (note, "printk" and "trace_printk" can also be used)
+ Currently, traceprintk flag cannot be used for memory
+ mapped ring buffers as described below.
+
+ trace_instance=foo^traceoff^traceprintk,sched,irq

The flags must come before the defined events.

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a79eefe84d6b..8e28f19f5316 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -500,6 +500,8 @@ static struct trace_array global_trace = {
.trace_flags = TRACE_DEFAULT_FLAGS,
};

+static struct trace_array *printk_trace = &global_trace;
+
void trace_set_ring_buffer_expanded(struct trace_array *tr)
{
if (!tr)
@@ -1117,7 +1119,7 @@ EXPORT_SYMBOL_GPL(__trace_array_puts);
*/
int __trace_puts(unsigned long ip, const char *str, int size)
{
- return __trace_array_puts(&global_trace, ip, str, size);
+ return __trace_array_puts(printk_trace, ip, str, size);
}
EXPORT_SYMBOL_GPL(__trace_puts);

@@ -1128,6 +1130,7 @@ EXPORT_SYMBOL_GPL(__trace_puts);
*/
int __trace_bputs(unsigned long ip, const char *str)
{
+ struct trace_array *tr = printk_trace;
struct ring_buffer_event *event;
struct trace_buffer *buffer;
struct bputs_entry *entry;
@@ -1135,14 +1138,14 @@ int __trace_bputs(unsigned long ip, const char *str)
int size = sizeof(struct bputs_entry);
int ret = 0;

- if (!(global_trace.trace_flags & TRACE_ITER_PRINTK))
+ if (!(tr->trace_flags & TRACE_ITER_PRINTK))
return 0;

if (unlikely(tracing_selftest_running || tracing_disabled))
return 0;

trace_ctx = tracing_gen_ctx();
- buffer = global_trace.array_buffer.buffer;
+ buffer = tr->array_buffer.buffer;

ring_buffer_nest_start(buffer);
event = __trace_buffer_lock_reserve(buffer, TRACE_BPUTS, size,
@@ -1155,7 +1158,7 @@ int __trace_bputs(unsigned long ip, const char *str)
entry->str = str;

__buffer_unlock_commit(buffer, event);
- ftrace_trace_stack(&global_trace, buffer, trace_ctx, 4, NULL);
+ ftrace_trace_stack(tr, buffer, trace_ctx, 4, NULL);

ret = 1;
out:
@@ -3025,7 +3028,7 @@ void trace_dump_stack(int skip)
/* Skip 1 to skip this function. */
skip++;
#endif
- __ftrace_trace_stack(global_trace.array_buffer.buffer,
+ __ftrace_trace_stack(printk_trace->array_buffer.buffer,
tracing_gen_ctx(), skip, NULL);
}
EXPORT_SYMBOL_GPL(trace_dump_stack);
@@ -3244,7 +3247,7 @@ int trace_vbprintk(unsigned long ip, const char *fmt, va_list args)
struct trace_event_call *call = &event_bprint;
struct ring_buffer_event *event;
struct trace_buffer *buffer;
- struct trace_array *tr = &global_trace;
+ struct trace_array *tr = printk_trace;
struct bprint_entry *entry;
unsigned int trace_ctx;
char *tbuffer;
@@ -3342,7 +3345,7 @@ __trace_array_vprintk(struct trace_buffer *buffer,
memcpy(&entry->buf, tbuffer, len + 1);
if (!call_filter_check_discard(call, entry, buffer, event)) {
__buffer_unlock_commit(buffer, event);
- ftrace_trace_stack(&global_trace, buffer, trace_ctx, 6, NULL);
+ ftrace_trace_stack(printk_trace, buffer, trace_ctx, 6, NULL);
}

out:
@@ -3438,7 +3441,7 @@ int trace_array_printk_buf(struct trace_buffer *buffer,
int ret;
va_list ap;

- if (!(global_trace.trace_flags & TRACE_ITER_PRINTK))
+ if (!(printk_trace->trace_flags & TRACE_ITER_PRINTK))
return 0;

va_start(ap, fmt);
@@ -3450,7 +3453,7 @@ int trace_array_printk_buf(struct trace_buffer *buffer,
__printf(2, 0)
int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
{
- return trace_array_vprintk(&global_trace, ip, fmt, args);
+ return trace_array_vprintk(printk_trace, ip, fmt, args);
}
EXPORT_SYMBOL_GPL(trace_vprintk);

@@ -9666,6 +9669,9 @@ static int __remove_instance(struct trace_array *tr)
set_tracer_flag(tr, 1 << i, 0);
}

+ if (printk_trace == tr)
+ printk_trace = &global_trace;
+
tracing_set_nop(tr);
clear_ftrace_function_probes(tr);
event_trace_del_tracer(tr);
@@ -10468,6 +10474,7 @@ __init static void enable_instances(void)
phys_addr_t start = 0;
phys_addr_t size = 0;
unsigned long addr = 0;
+ bool traceprintk = false;
bool traceoff = false;
char *flag_delim;
char *addr_delim;
@@ -10489,11 +10496,16 @@ __init static void enable_instances(void)
char *flag;

while ((flag = strsep(&flag_delim, "^"))) {
- if (strcmp(flag, "traceoff") == 0)
+ if (strcmp(flag, "traceoff") == 0) {
traceoff = true;
- else
+ } else if ((strcmp(flag, "printk") == 0) ||
+ (strcmp(flag, "traceprintk") == 0) ||
+ (strcmp(flag, "trace_printk") == 0)) {
+ traceprintk = true;
+ } else {
pr_info("Tracing: Invalid instance flag '%s' for %s\n",
flag, name);
+ }
}
}

@@ -10548,6 +10560,18 @@ __init static void enable_instances(void)
if (traceoff)
tracer_tracing_off(tr);

+ if (traceprintk) {
+ /*
+ * The binary format of traceprintk can cause a crash if used
+ * by a buffer from another boot. Do not allow it for the
+ * memory mapped ring buffers.
+ */
+ if (start)
+ pr_warn("Tracing: WARNING: memory mapped ring buffers cannot be used for trace_printk\n");
+ else
+ printk_trace = tr;
+ }
+
/* Only allow non mapped buffers to be deleted */
if (!start)