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

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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 <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vineeth Pillai <vineeth@bitbyteword.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Alexander Aring <aahringo@redhat.com>
Cc: "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>
Cc: Tomas Glozar <tglozar@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Jonathan Corbet" <corbet@lwn.net>
Link: https://lore.kernel.org/20240823014019.053229958@goodmis.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2024-08-22 21:39:03 -04:00 committed by Steven Rostedt (Google)
parent eb2dcde9f9
commit b6fc31b687
2 changed files with 47 additions and 1 deletions
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17
Documentation/admin-guide/kernel-parameters.txt
View File

@ -6743,6 +6743,15 @@
the same thing would happen if it was left off). The irq_handler_entry
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.
trace_instance=foo^traceoff,sched,irq
The flags must come before the defined events.
If memory has been reserved (see memmap for x86), the instance
can use that memory:
@ -6765,6 +6774,14 @@
kernel versions where the validator will fail and reset the ring buffer
if the layout is not the same as the previous kernel.
If the ring buffer is used for persistent bootups and has events enabled,
it is recommend to disable tracing so that events from a previous boot do not
mix with events of the current boot (unless you are debugging a random crash
at boot up).
reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff@trace,sched,irq
trace_options=[option-list]
[FTRACE] Enable or disable tracer options at boot.
The option-list is a comma delimited list of options

31
kernel/trace/trace.c
View File

@ -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);