tracing/function-graph-tracer: prevent hangs during self-tests
Impact: detect tracing related hangs
Sometimes, with some configs, the function graph tracer can make
the timer interrupt too much slow, hanging the kernel in an endless
loop of timer interrupts servicing.
As suggested by Ingo, this patch brings a watchdog which stops the
selftest after a defined number of functions traced, definitely
disabling this tracer.
For those who want to debug the cause of the function graph trace
hang, you can pass the ftrace_dump_on_oops kernel parameter to dump
the traces after this hang detection.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1237694675-23509-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e3dfefe..e6fac0f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4018,11 +4018,12 @@
trace_seq_init(s);
}
-void ftrace_dump(void)
+static void __ftrace_dump(bool disable_tracing)
{
static DEFINE_SPINLOCK(ftrace_dump_lock);
/* use static because iter can be a bit big for the stack */
static struct trace_iterator iter;
+ unsigned int old_userobj;
static int dump_ran;
unsigned long flags;
int cnt = 0, cpu;
@@ -4034,14 +4035,17 @@
dump_ran = 1;
- /* No turning back! */
tracing_off();
- ftrace_kill();
+
+ if (disable_tracing)
+ ftrace_kill();
for_each_tracing_cpu(cpu) {
atomic_inc(&global_trace.data[cpu]->disabled);
}
+ old_userobj = trace_flags & TRACE_ITER_SYM_USEROBJ;
+
/* don't look at user memory in panic mode */
trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
@@ -4086,10 +4090,26 @@
else
printk(KERN_TRACE "---------------------------------\n");
+ /* Re-enable tracing if requested */
+ if (!disable_tracing) {
+ trace_flags |= old_userobj;
+
+ for_each_tracing_cpu(cpu) {
+ atomic_dec(&global_trace.data[cpu]->disabled);
+ }
+ tracing_on();
+ }
+
out:
spin_unlock_irqrestore(&ftrace_dump_lock, flags);
}
+/* By default: disable tracing after the dump */
+void ftrace_dump(void)
+{
+ __ftrace_dump(true);
+}
+
__init static int tracer_alloc_buffers(void)
{
struct trace_array_cpu *data;