tracing: Fix ent_size in trace output

When reading the trace file, the records of each of the per_cpu buffers
are examined to find the next event to print out. At the point of looking
at the event, the size of the event is recorded. But if the first event is
chosen, the other events in the other CPU buffers will reset the event size
that is stored in the iterator descriptor, causing the event size passed to
the output functions to be incorrect.

In most cases this is not a problem, but for the case of stack traces, it
is. With the change to the stack tracing to record a dynamic number of
back traces, the output depends on the size of the entry instead of the
fixed 8 back traces. When the entry size is not correct, the back traces
would not be fully printed.

Note, reading from the per-cpu trace files were not affected.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3a19c354edd6b50fd21d2e1e1be5273f128781f7..ed7b5d1e12f468168178b1a3c144d9736e0b4614 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1698,6 +1698,7 @@ __find_next_entry(struct trace_iterator *iter, int *ent_cpu,
        int cpu_file = iter->cpu_file;
        u64 next_ts = 0, ts;
        int next_cpu = -1;
+       int next_size = 0;
        int cpu;
 
        /*
@@ -1729,9 +1730,12 @@ __find_next_entry(struct trace_iterator *iter, int *ent_cpu,
                        next_cpu = cpu;
                        next_ts = ts;
                        next_lost = lost_events;
+                       next_size = iter->ent_size;
                }
        }
 
+       iter->ent_size = next_size;
+
        if (ent_cpu)
                *ent_cpu = next_cpu;