tracing: report error in trace if we fail to swap latency buffer
The irqsoff tracer will fail to swap the cpu buffer with the max
buffer if it preempts a commit. Instead of ignoring this, this patch
makes the tracer report it if the last max latency failed due to preempting
a current commit.
The output of the latency tracer will look like this:
# tracer: irqsoff
#
# irqsoff latency trace v1.1.5 on 2.6.31-rc5
# --------------------------------------------------------------------
# latency: 112 us, #1/1, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
# -----------------
# | task: -4281 (uid:0 nice:0 policy:0 rt_prio:0)
# -----------------
# => started at: save_args
# => ended at: __do_softirq
#
#
# _------=> CPU#
# / _-----=> irqs-off
# | / _----=> need-resched
# || / _---=> hardirq/softirq
# ||| / _--=> preempt-depth
# |||| /
# ||||| delay
# cmd pid ||||| time | caller
# \ / ||||| \ | /
bash-4281 1d.s6 265us : update_max_tr_single: Failed to swap buffers due to commit in progress
Note the latency time and the functions that disabled the irqs or preemption
will still be listed.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ef08328..6df9861 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -482,9 +482,20 @@
ret = ring_buffer_swap_cpu(max_tr.buffer, tr->buffer, cpu);
+ if (ret == -EBUSY) {
+ /*
+ * We failed to swap the buffer due to a commit taking
+ * place on this CPU. We fail to record, but we reset
+ * the max trace buffer (no one writes directly to it)
+ * and flag that it failed.
+ */
+ trace_array_printk(&max_tr, _THIS_IP_,
+ "Failed to swap buffers due to commit in progress\n");
+ }
+
ftrace_enable_cpu();
- WARN_ON_ONCE(ret && ret != -EAGAIN);
+ WARN_ON_ONCE(ret && ret != -EAGAIN && ret != -EBUSY);
__update_max_tr(tr, tsk, cpu);
__raw_spin_unlock(&ftrace_max_lock);