Commit de7edd31 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
Browse files

tracing: Disable tracing on warning 



Add a traceoff_on_warning option in both the kernel command line as well
as a sysctl option. When set, any WARN*() function that is hit will cause
the tracing_on variable to be cleared, which disables writing to the
ring buffer.

This is useful especially when tracing a bug with function tracing. When
a warning is hit, the print caused by the warning can flood the trace with
the functions that producing the output for the warning. This can make the
resulting trace useless by either hiding where the bug happened, or worse,
by overflowing the buffer and losing the trace of the bug totally.

Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent c3e13c7c

Documentation/kernel-parameters.txt

+13 −0
Original line number Diff line number Diff line
@@ -3069,6 +3069,19 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			See also Documentation/trace/ftrace.txt "trace options"

			section.



	traceoff_on_warning

			[FTRACE] enable this option to disable tracing when a

			warning is hit. This turns off "tracing_on". Tracing can

			be enabled again by echoing '1' into the "tracing_on"

			file located in /sys/kernel/debug/tracing/



			This option is useful, as it disables the trace before

			the WARNING dump is called, which prevents the trace to

			be filled with content caused by the warning output.



			This option can also be set at run time via the sysctl

			option:  kernel/traceoff_on_warning



	transparent_hugepage=

			[KNL]

			Format: [always|madvise|never]

include/linux/ftrace.h

+5 −0
Original line number Diff line number Diff line
@@ -824,10 +824,15 @@ enum ftrace_dump_mode; 


extern enum ftrace_dump_mode ftrace_dump_on_oops;



extern void disable_trace_on_warning(void);

extern int __disable_trace_on_warning;



#ifdef CONFIG_PREEMPT

#define INIT_TRACE_RECURSION		.trace_recursion = 0,

#endif



#else /* CONFIG_TRACING */

static inline void  disable_trace_on_warning(void) { }

#endif /* CONFIG_TRACING */



#ifndef INIT_TRACE_RECURSION

kernel/panic.c

+3 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/notifier.h>

#include <linux/module.h>

#include <linux/random.h>

#include <linux/ftrace.h>

#include <linux/reboot.h>

#include <linux/delay.h>

#include <linux/kexec.h>
@@ -399,6 +400,8 @@ struct slowpath_args { 
static void warn_slowpath_common(const char *file, int line, void *caller,

				 unsigned taint, struct slowpath_args *args)

{

	disable_trace_on_warning();



	printk(KERN_WARNING "------------[ cut here ]------------\n");

	printk(KERN_WARNING "WARNING: at %s:%d %pS()\n", file, line, caller);

kernel/sysctl.c

+7 −0
Original line number Diff line number Diff line
@@ -600,6 +600,13 @@ static struct ctl_table kern_table[] = { 
		.mode		= 0644,

		.proc_handler	= proc_dointvec,

	},

	{

		.procname	= "traceoff_on_warning",

		.data		= &__disable_trace_on_warning,

		.maxlen		= sizeof(__disable_trace_on_warning),

		.mode		= 0644,

		.proc_handler	= proc_dointvec,

	},

#endif

#ifdef CONFIG_MODULES

	{

kernel/trace/trace.c

+17 −0
Original line number Diff line number Diff line
@@ -115,6 +115,9 @@ cpumask_var_t __read_mostly tracing_buffer_mask; 


enum ftrace_dump_mode ftrace_dump_on_oops;



/* When set, tracing will stop when a WARN*() is hit */

int __disable_trace_on_warning;



static int tracing_set_tracer(const char *buf);



#define MAX_TRACER_SIZE		100
@@ -149,6 +152,13 @@ static int __init set_ftrace_dump_on_oops(char *str) 
}

__setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);



static int __init stop_trace_on_warning(char *str)

{

	__disable_trace_on_warning = 1;

	return 1;

}

__setup("traceoff_on_warning=", stop_trace_on_warning);



static int __init boot_alloc_snapshot(char *str)

{

	allocate_snapshot = true;
@@ -170,6 +180,7 @@ static int __init set_trace_boot_options(char *str) 
}

__setup("trace_options=", set_trace_boot_options);





unsigned long long ns2usecs(cycle_t nsec)

{

	nsec += 500;
@@ -562,6 +573,12 @@ void tracing_off(void) 
}

EXPORT_SYMBOL_GPL(tracing_off);



void disable_trace_on_warning(void)

{

	if (__disable_trace_on_warning)

		tracing_off();

}



/**

 * tracing_is_on - show state of ring buffers enabled

 */

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