tracing: Fix polling on trace_pipe_raw

The trace_pipe_raw never implemented polling and this was casing
issues for several utilities. This is now implemented.

Blocked reads still are on the TODO list.

Reported-by: Mauro Carvalho Chehab <[e-mail]>
Tested-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: Steven Rostedt <[e-mail]>

kernel/trace/trace.c

···
 }
 
 static unsigned int
-tracing_poll_pipe(struct file *filp, poll_table *poll_table)
+trace_poll(struct trace_iterator *iter, struct file *filp, poll_table *poll_table)
 {
-	struct trace_iterator *iter = filp->private_data;
-
 	if (trace_flags & TRACE_ITER_BLOCK) {
 		/*
 		 * Always select as readable when in blocking mode
···
 	} else {
 		if (!trace_empty(iter))
 			return POLLIN | POLLRDNORM;
+		trace_wakeup_needed = true;
 		poll_wait(filp, &trace_wait, poll_table);
 		if (!trace_empty(iter))
 			return POLLIN | POLLRDNORM;
 
 		return 0;
 	}
+}
+
+static unsigned int
+tracing_poll_pipe(struct file *filp, poll_table *poll_table)
+{
+	struct trace_iterator *iter = filp->private_data;
+
+	return trace_poll(iter, filp, poll_table);
 }
 
 /*
···
 #endif /* CONFIG_TRACER_SNAPSHOT */
 
 struct ftrace_buffer_info {
-	struct trace_array	*tr;
+	struct trace_iterator	iter;
 	void			*spare;
-	int			cpu;
 	unsigned int		read;
 };
 
···
 	if (!info)
 		return -ENOMEM;
 
-	info->tr	= tr;
-	info->cpu	= tc->cpu;
-	info->spare	= NULL;
+	info->iter.tr		= tr;
+	info->iter.cpu_file	= tc->cpu;
+	info->spare		= NULL;
 	/* Force reading ring buffer for first read */
-	info->read	= (unsigned int)-1;
+	info->read		= (unsigned int)-1;
 
 	filp->private_data = info;
 
 	return nonseekable_open(inode, filp);
+}
+
+static unsigned int
+tracing_buffers_poll(struct file *filp, poll_table *poll_table)
+{
+	struct ftrace_buffer_info *info = filp->private_data;
+	struct trace_iterator *iter = &info->iter;
+
+	return trace_poll(iter, filp, poll_table);
 }
 
 static ssize_t
···
 		     size_t count, loff_t *ppos)
 {
 	struct ftrace_buffer_info *info = filp->private_data;
+	struct trace_iterator *iter = &info->iter;
 	ssize_t ret;
 	size_t size;
 
···
 		return 0;
 
 	if (!info->spare)
-		info->spare = ring_buffer_alloc_read_page(info->tr->buffer, info->cpu);
+		info->spare = ring_buffer_alloc_read_page(iter->tr->buffer, iter->cpu_file);
 	if (!info->spare)
 		return -ENOMEM;
 
···
 	if (info->read < PAGE_SIZE)
 		goto read;
 
-	trace_access_lock(info->cpu);
-	ret = ring_buffer_read_page(info->tr->buffer,
+	trace_access_lock(iter->cpu_file);
+	ret = ring_buffer_read_page(iter->tr->buffer,
 				    &info->spare,
 				    count,
-				    info->cpu, 0);
-	trace_access_unlock(info->cpu);
+				    iter->cpu_file, 0);
+	trace_access_unlock(iter->cpu_file);
 	if (ret < 0)
 		return 0;
 
···
 static int tracing_buffers_release(struct inode *inode, struct file *file)
 {
 	struct ftrace_buffer_info *info = file->private_data;
+	struct trace_iterator *iter = &info->iter;
 
 	if (info->spare)
-		ring_buffer_free_read_page(info->tr->buffer, info->spare);
+		ring_buffer_free_read_page(iter->tr->buffer, info->spare);
 	kfree(info);
 
 	return 0;
···
 			    unsigned int flags)
 {
 	struct ftrace_buffer_info *info = file->private_data;
+	struct trace_iterator *iter = &info->iter;
 	struct partial_page partial_def[PIPE_DEF_BUFFERS];
 	struct page *pages_def[PIPE_DEF_BUFFERS];
 	struct splice_pipe_desc spd = {
···
 		len &= PAGE_MASK;
 	}
 
-	trace_access_lock(info->cpu);
-	entries = ring_buffer_entries_cpu(info->tr->buffer, info->cpu);
+ again:
+	trace_access_lock(iter->cpu_file);
+	entries = ring_buffer_entries_cpu(iter->tr->buffer, iter->cpu_file);
 
 	for (i = 0; i < pipe->buffers && len && entries; i++, len -= PAGE_SIZE) {
 		struct page *page;
···
 			break;
 
 		ref->ref = 1;
-		ref->buffer = info->tr->buffer;
-		ref->page = ring_buffer_alloc_read_page(ref->buffer, info->cpu);
+		ref->buffer = iter->tr->buffer;
+		ref->page = ring_buffer_alloc_read_page(ref->buffer, iter->cpu_file);
 		if (!ref->page) {
 			kfree(ref);
 			break;
 		}
 
 		r = ring_buffer_read_page(ref->buffer, &ref->page,
-					  len, info->cpu, 1);
+					  len, iter->cpu_file, 1);
 		if (r < 0) {
 			ring_buffer_free_read_page(ref->buffer, ref->page);
 			kfree(ref);
···
 		spd.nr_pages++;
 		*ppos += PAGE_SIZE;
 
-		entries = ring_buffer_entries_cpu(info->tr->buffer, info->cpu);
+		entries = ring_buffer_entries_cpu(iter->tr->buffer, iter->cpu_file);
 	}
 
-	trace_access_unlock(info->cpu);
+	trace_access_unlock(iter->cpu_file);
 	spd.nr_pages = i;
 
 	/* did we read anything? */
 	if (!spd.nr_pages) {
-		if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))
+		if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK)) {
 			ret = -EAGAIN;
-		else
-			ret = 0;
-		/* TODO: block */
-		goto out;
+			goto out;
+		}
+		default_wait_pipe(iter);
+		if (signal_pending(current)) {
+			ret = -EINTR;
+			goto out;
+		}
+		goto again;
 	}
 
 	ret = splice_to_pipe(pipe, &spd);
···
 static const struct file_operations tracing_buffers_fops = {
 	.open		= tracing_buffers_open,
 	.read		= tracing_buffers_read,
+	.poll		= tracing_buffers_poll,
 	.release	= tracing_buffers_release,
 	.splice_read	= tracing_buffers_splice_read,
 	.llseek		= no_llseek,