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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/panic.c b/kernel/panic.c
index 167ec097..4cea6cc 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -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 @@
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);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 9edcf45..5b0f18c 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -600,6 +600,13 @@
.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
{
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5f4a09c..c4c9296 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -115,6 +115,9 @@
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 @@
}
__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 @@
}
__setup("trace_options=", set_trace_boot_options);
+
unsigned long long ns2usecs(cycle_t nsec)
{
nsec += 500;
@@ -562,6 +573,12 @@
}
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
*/
