tracing: Fix read blocking on trace_pipe_raw

If the ring buffer is empty, a read to trace_pipe_raw wont block.
The tracing code has the infrastructure to wake up waiting readers,
but the trace_pipe_raw doesn't take advantage of that.

When a read is done to trace_pipe_raw without the O_NONBLOCK flag
set, have the read block until there's data in the requested buffer.

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

1 files changed, 15 insertions, 3 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4a6e461273a9..3ec146c96df4 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4389,6 +4389,7 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)
 
         info->iter.tr           = tr;
         info->iter.cpu_file     = tc->cpu;
+        info->iter.trace        = tr->current_trace;
         info->spare             = NULL;
         /* Force reading ring buffer for first read */
         info->read              = (unsigned int)-1;
@@ -4428,18 +4429,29 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
         if (info->read < PAGE_SIZE)
                 goto read;
 
+ again:
         trace_access_lock(iter->cpu_file);
         ret = ring_buffer_read_page(iter->tr->buffer,
                                     &info->spare,
                                     count,
                                     iter->cpu_file, 0);
         trace_access_unlock(iter->cpu_file);
-        if (ret < 0)
+
+        if (ret < 0) {
+                if (trace_empty(iter)) {
+                        if ((filp->f_flags & O_NONBLOCK))
+                                return -EAGAIN;
+                        iter->trace->wait_pipe(iter);
+                        if (signal_pending(current))
+                                return -EINTR;
+                        goto again;
+                }
                 return 0;
+        }
 
         info->read = 0;
 
-read:
+ read:
         size = PAGE_SIZE - info->read;
         if (size > count)
                 size = count;
@@ -4616,7 +4628,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
                         ret = -EAGAIN;
                         goto out;
                 }
-                default_wait_pipe(iter);
+                iter->trace->wait_pipe(iter);
                 if (signal_pending(current)) {
                         ret = -EINTR;
                         goto out;