ftrace: add logic to record overruns

This patch sets up the infrastructure to record overruns of the tracing
buffer.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 16 insertions, 6 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1281969103b8..b9126ef46a9e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -609,6 +609,7 @@ void unregister_tracer(struct tracer *type)
 void tracing_reset(struct trace_array_cpu *data)
 {
         data->trace_idx = 0;
+        data->overrun = 0;
         data->trace_head = data->trace_tail = head_page(data);
         data->trace_head_idx = 0;
         data->trace_tail_idx = 0;
@@ -750,6 +751,7 @@ tracing_get_trace_entry(struct trace_array *tr, struct trace_array_cpu *data)
         if (data->trace_head == data->trace_tail &&
             idx_next == data->trace_tail_idx) {
                 /* overrun */
+                data->overrun++;
                 data->trace_tail_idx++;
                 if (data->trace_tail_idx >= ENTRIES_PER_PAGE) {
                         data->trace_tail =
@@ -2353,8 +2355,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 {
         struct trace_iterator *iter = filp->private_data;
         struct trace_array_cpu *data;
-        struct trace_array *tr = iter->tr;
-        struct tracer *tracer = iter->trace;
         static cpumask_t mask;
         static int start;
         unsigned long flags;
@@ -2433,10 +2433,11 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         if (cnt >= PAGE_SIZE)
                 cnt = PAGE_SIZE - 1;
 
-        memset(iter, 0, sizeof(*iter));
-        iter->tr = tr;
-        iter->trace = tracer;
+        /* reset all but tr, trace, and overruns */
         iter->pos = -1;
+        memset(&iter->seq, 0,
+               sizeof(struct trace_iterator) -
+               offsetof(struct trace_iterator, seq));
 
         /*
          * We need to stop all tracing on all CPUS to read the
@@ -2465,6 +2466,11 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         for_each_cpu_mask(cpu, mask) {
                 data = iter->tr->data[cpu];
                 __raw_spin_lock(&data->lock);
+
+                if (data->overrun > iter->last_overrun[cpu])
+                        iter->overrun[cpu] +=
+                                data->overrun - iter->last_overrun[cpu];
+                iter->last_overrun[cpu] = data->overrun;
         }
 
         while (find_next_entry_inc(iter) != NULL) {
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8991c5efcc74..c1ec134ac356 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -97,6 +97,7 @@ struct trace_array_cpu {
         void                    *trace_head; /* producer */
         void                    *trace_tail; /* consumer */
         unsigned long           trace_idx;
+        unsigned long           overrun;
         unsigned long           saved_latency;
         unsigned long           critical_start;
         unsigned long           critical_end;
@@ -157,10 +158,13 @@ struct trace_seq {
  * results to users and which routines might sleep, etc:
  */
 struct trace_iterator {
-        struct trace_seq        seq;
         struct trace_array      *tr;
         struct tracer           *trace;
+        long                    last_overrun[NR_CPUS];
+        long                    overrun[NR_CPUS];
 
+        /* The below is zeroed out in pipe_read */
+        struct trace_seq        seq;
         struct trace_entry      *ent;
         int                     cpu;