tracing: Have stack trace not record if RCU is not watching

The stack tracer records a stack dump whenever it sees a stack usage that is
more than what it ever saw before. This can happen at any function that is
being traced. If it happens when the CPU is going idle (or other strange
locations), RCU may not be watching, and in this case, the recording of the
stack trace will trigger a warning. There's been lots of efforts to make
hacks to allow stack tracing to proceed even if RCU is not watching, but
this only causes more issues to appear. Simply do not trace a stack if RCU
is not watching. It probably isn't a bad stack anyway.

Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 734accc02418930280a5248013fa6fbd4a5868e2..3c7bfc4bf5e9981b687ca8dd4ed1cf890b38ee12 100644 (file)
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -209,6 +209,10 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
        if (__this_cpu_read(disable_stack_tracer) != 1)
                goto out;
 
+       /* If rcu is not watching, then save stack trace can fail */
+       if (!rcu_is_watching())
+               goto out;
+
        ip += MCOUNT_INSN_SIZE;
 
        check_stack(ip, &stack);