tracing: Add "traceoff" flag to boot time tracing instances

Add a "flags" delimiter (^) to the "trace_instance" kernel command line
parameter, and add the "traceoff" flag. The format is:

   trace_instance=<name>[^<flag1>[^<flag2>]][@<memory>][,<events>]

The code allows for more than one flag to be added, but currently only
"traceoff" is done so.

The motivation for this change came from debugging with the persistent
ring buffer and having trace_printk() writing to it. The trace_printk
calls are always enabled, and the boot after the crash was having the
unwanted trace_printks from the current boot inject into the ring buffer
with the trace_printks of the crash kernel, making the output very
confusing.

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Vincent Donnefort <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vineeth Pillai <[email protected]>
Cc: Beau Belgrave <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: David Howells <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Alexander Aring <[email protected]>
Cc: "Luis Claudio R. Goncalves" <[email protected]>
Cc: Tomas Glozar <[email protected]>
Cc: John Kacur <[email protected]>
Cc: Clark Williams <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: "Jonathan Corbet" <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Steven Rostedt (Google) <[email protected]>

1 files changed, 30 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9bcef199ae90..a79eefe84d6b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -10468,10 +10468,36 @@ __init static void enable_instances(void)
 		phys_addr_t start = 0;
 		phys_addr_t size = 0;
 		unsigned long addr = 0;
+		bool traceoff = false;
+		char *flag_delim;
+		char *addr_delim;
 
 		tok = strsep(&curr_str, ",");
-		name = strsep(&tok, "@");
 
+		flag_delim = strchr(tok, '^');
+		addr_delim = strchr(tok, '@');
+
+		if (addr_delim)
+			*addr_delim++ = '\0';
+
+		if (flag_delim)
+			*flag_delim++ = '\0';
+
+		name = tok;
+
+		if (flag_delim) {
+			char *flag;
+
+			while ((flag = strsep(&flag_delim, "^"))) {
+				if (strcmp(flag, "traceoff") == 0)
+					traceoff = true;
+				else
+					pr_info("Tracing: Invalid instance flag '%s' for %s\n",
+						flag, name);
+			}
+		}
+
+		tok = addr_delim;
 		if (tok && isdigit(*tok)) {
 			start = memparse(tok, &tok);
 			if (!start) {
@@ -10519,6 +10545,9 @@ __init static void enable_instances(void)
 			continue;
 		}
 
+		if (traceoff)
+			tracer_tracing_off(tr);
+
 		/* Only allow non mapped buffers to be deleted */
 		if (!start)
 			trace_array_put(tr);