tracing: pass around ring buffer instead of tracer

The latency tracers (irqsoff and wakeup) can swap trace buffers
on the fly. If an event is happening and has reserved data on one of
the buffers, and the latency tracer swaps the global buffer with the
max buffer, the result is that the event may commit the data to the
wrong buffer.

This patch changes the API to the trace recording to be recieve the
buffer that was used to reserve a commit. Then this buffer can be passed
in to the commit.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 1090b0aed9ba..243bafc2ec90 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -65,13 +65,15 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
 {
         struct blk_io_trace *t;
         struct ring_buffer_event *event = NULL;
+        struct ring_buffer *buffer = NULL;
         int pc = 0;
         int cpu = smp_processor_id();
         bool blk_tracer = blk_tracer_enabled;
 
         if (blk_tracer) {
+                buffer = blk_tr->buffer;
                 pc = preempt_count();
-                event = trace_buffer_lock_reserve(blk_tr, TRACE_BLK,
+                event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
                                                   sizeof(*t) + len,
                                                   0, pc);
                 if (!event)
@@ -96,7 +98,7 @@ record_it:
                 memcpy((void *) t + sizeof(*t), data, len);
 
                 if (blk_tracer)
-                        trace_buffer_unlock_commit(blk_tr, event, 0, pc);
+                        trace_buffer_unlock_commit(buffer, event, 0, pc);
         }
 }
 
@@ -179,6 +181,7 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 {
         struct task_struct *tsk = current;
         struct ring_buffer_event *event = NULL;
+        struct ring_buffer *buffer = NULL;
         struct blk_io_trace *t;
         unsigned long flags = 0;
         unsigned long *sequence;
@@ -204,8 +207,9 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
         if (blk_tracer) {
                 tracing_record_cmdline(current);
 
+                buffer = blk_tr->buffer;
                 pc = preempt_count();
-                event = trace_buffer_lock_reserve(blk_tr, TRACE_BLK,
+                event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
                                                   sizeof(*t) + pdu_len,
                                                   0, pc);
                 if (!event)
@@ -252,7 +256,7 @@ record_it:
                         memcpy((void *) t + sizeof(*t), pdu_data, pdu_len);
 
                 if (blk_tracer) {
-                        trace_buffer_unlock_commit(blk_tr, event, 0, pc);
+                        trace_buffer_unlock_commit(buffer, event, 0, pc);
                         return;
                 }
         }