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Subject[for-next-3.11][PATCH 4/4] tracing: Fix reset of time stamps during trace_clock changes
From: Alexander Z Lam <azl@google.com>

Fixed two issues with changing the timestamp clock with trace_clock:

- The global buffer was reset on instance clock changes. Change this to pass
the correct per-instance buffer
- ftrace_now() is used to set buf->time_start in tracing_reset_online_cpus().
This was incorrect because ftrace_now() used the global buffer's clock to
return the current time. Change this to use buffer_ftrace_now() which
returns the current time for the correct per-instance buffer.

Also removed tracing_reset_current() because it is not used anywhere

Link: http://lkml.kernel.org/r/1375493777-17261-2-git-send-email-azl@google.com

Cc: Vaibhav Nagarnaik <vnagarnaik@google.com>
Cc: David Sharp <dhsharp@google.com>
Cc: Alexander Z Lam <lambchop468@gmail.com>
Cc: stable@vger.kernel.org # 3.10
Signed-off-by: Alexander Z Lam <azl@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 531c9e6..496f94d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -243,20 +243,25 @@ int filter_current_check_discard(struct ring_buffer *buffer,
}
EXPORT_SYMBOL_GPL(filter_current_check_discard);

-cycle_t ftrace_now(int cpu)
+cycle_t buffer_ftrace_now(struct trace_buffer *buf, int cpu)
{
u64 ts;

/* Early boot up does not have a buffer yet */
- if (!global_trace.trace_buffer.buffer)
+ if (!buf->buffer)
return trace_clock_local();

- ts = ring_buffer_time_stamp(global_trace.trace_buffer.buffer, cpu);
- ring_buffer_normalize_time_stamp(global_trace.trace_buffer.buffer, cpu, &ts);
+ ts = ring_buffer_time_stamp(buf->buffer, cpu);
+ ring_buffer_normalize_time_stamp(buf->buffer, cpu, &ts);

return ts;
}

+cycle_t ftrace_now(int cpu)
+{
+ return buffer_ftrace_now(&global_trace.trace_buffer, cpu);
+}
+
/**
* tracing_is_enabled - Show if global_trace has been disabled
*
@@ -1211,7 +1216,7 @@ void tracing_reset_online_cpus(struct trace_buffer *buf)
/* Make sure all commits have finished */
synchronize_sched();

- buf->time_start = ftrace_now(buf->cpu);
+ buf->time_start = buffer_ftrace_now(buf, buf->cpu);

for_each_online_cpu(cpu)
ring_buffer_reset_cpu(buffer, cpu);
@@ -1219,11 +1224,6 @@ void tracing_reset_online_cpus(struct trace_buffer *buf)
ring_buffer_record_enable(buffer);
}

-void tracing_reset_current(int cpu)
-{
- tracing_reset(&global_trace.trace_buffer, cpu);
-}
-
/* Must have trace_types_lock held */
void tracing_reset_all_online_cpus(void)
{
@@ -4634,12 +4634,12 @@ static ssize_t tracing_clock_write(struct file *filp, const char __user *ubuf,
* New clock may not be consistent with the previous clock.
* Reset the buffer so that it doesn't have incomparable timestamps.
*/
- tracing_reset_online_cpus(&global_trace.trace_buffer);
+ tracing_reset_online_cpus(&tr->trace_buffer);

#ifdef CONFIG_TRACER_MAX_TRACE
if (tr->flags & TRACE_ARRAY_FL_GLOBAL && tr->max_buffer.buffer)
ring_buffer_set_clock(tr->max_buffer.buffer, trace_clocks[i].func);
- tracing_reset_online_cpus(&global_trace.max_buffer);
+ tracing_reset_online_cpus(&tr->max_buffer);
#endif

mutex_unlock(&trace_types_lock);
--
1.7.10.4



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