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tracing: Add tp_printk_stop_on_boot option 

Add a kernel command line option that disables printing of events to
console at late_initcall_sync(). This is useful when needing to see
specific events written to console on boot up, but not wanting it when
user space starts, as user space may make the console so noisy that the
system becomes inoperable.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2021-06-17 10:51:02 -04:00
parent 8f0901cda1
commit f38601368f
2 changed files with 42 additions and 11 deletions
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13
Documentation/admin-guide/kernel-parameters.txt
View File

@ -5605,12 +5605,25 @@
Note, echoing 1 into this file without the
tracepoint_printk kernel cmdline option has no effect.
The tp_printk_stop_on_boot (see below) can also be used
to stop the printing of events to console at
late_initcall_sync.
** CAUTION **
Having tracepoints sent to printk() and activating high
frequency tracepoints such as irq or sched, can cause
the system to live lock.
tp_printk_stop_on_boot[FTRACE]
When tp_printk (above) is set, it can cause a lot of noise
on the console. It may be useful to only include the
printing of events during boot up, as user space may
make the system inoperable.
This command line option will stop the printing of events
to console at the late_initcall_sync() time frame.
traceoff_on_warning
[FTRACE] enable this option to disable tracing when a
warning is hit. This turns off "tracing_on". Tracing can

40
kernel/trace/trace.c
View File

@ -86,6 +86,7 @@ void __init disable_tracing_selftest(const char *reason)
/* Pipe tracepoints to printk */
struct trace_iterator *tracepoint_print_iter;
int tracepoint_printk;
static bool tracepoint_printk_stop_on_boot __initdata;
static DEFINE_STATIC_KEY_FALSE(tracepoint_printk_key);
/* For tracers that don't implement custom flags */
@ -256,6 +257,13 @@ static int __init set_tracepoint_printk(char *str)
}
__setup("tp_printk", set_tracepoint_printk);
static int __init set_tracepoint_printk_stop(char *str)
{
tracepoint_printk_stop_on_boot = true;
return 1;
}
__setup("tp_printk_stop_on_boot", set_tracepoint_printk_stop);
unsigned long long ns2usecs(u64 nsec)
{
nsec += 500;
@ -9578,6 +9586,8 @@ static __init int tracer_init_tracefs(void)
return 0;
}
fs_initcall(tracer_init_tracefs);
static int trace_panic_handler(struct notifier_block *this,
unsigned long event, void *unused)
{
@ -9998,7 +10008,7 @@ void __init trace_init(void)
trace_event_init();
}
__init static int clear_boot_tracer(void)
__init static void clear_boot_tracer(void)
{
/*
* The default tracer at boot buffer is an init section.
@ -10008,26 +10018,21 @@ __init static int clear_boot_tracer(void)
* about to be freed.
*/
if (!default_bootup_tracer)
return 0;
return;
printk(KERN_INFO "ftrace bootup tracer '%s' not registered.\n",
default_bootup_tracer);
default_bootup_tracer = NULL;
return 0;
}
fs_initcall(tracer_init_tracefs);
late_initcall_sync(clear_boot_tracer);
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
__init static int tracing_set_default_clock(void)
__init static void tracing_set_default_clock(void)
{
/* sched_clock_stable() is determined in late_initcall */
if (!trace_boot_clock && !sched_clock_stable()) {
if (security_locked_down(LOCKDOWN_TRACEFS)) {
pr_warn("Can not set tracing clock due to lockdown\n");
return -EPERM;
return;
}
printk(KERN_WARNING
@ -10037,8 +10042,21 @@ __init static int tracing_set_default_clock(void)
"on the kernel command line\n");
tracing_set_clock(&global_trace, "global");
}
}
#else
static inline void tracing_set_default_clock(void) { }
#endif
__init static int late_trace_init(void)
{
if (tracepoint_printk && tracepoint_printk_stop_on_boot) {
static_key_disable(&tracepoint_printk_key.key);
tracepoint_printk = 0;
}
tracing_set_default_clock();
clear_boot_tracer();
return 0;
}
late_initcall_sync(tracing_set_default_clock);
#endif
late_initcall_sync(late_trace_init);