1 files changed, 94 insertions, 64 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 3103a484182e..09df645ab9c7 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -834,51 +834,24 @@ static bool rb_watermark_hit(struct trace_buffer *buffer, int cpu, int full)
 		pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
 		ret = !pagebusy && full_hit(buffer, cpu, full);
 
-		if (!cpu_buffer->shortest_full ||
-		    cpu_buffer->shortest_full > full)
-			cpu_buffer->shortest_full = full;
+		if (!ret && (!cpu_buffer->shortest_full ||
+			     cpu_buffer->shortest_full > full)) {
+		    cpu_buffer->shortest_full = full;
+		}
 		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 	}
 	return ret;
 }
 
-/**
- * ring_buffer_wait - wait for input to the ring buffer
- * @buffer: buffer to wait on
- * @cpu: the cpu buffer to wait on
- * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
- *
- * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
- * as data is added to any of the @buffer's cpu buffers. Otherwise
- * it will wait for data to be added to a specific cpu buffer.
- */
-int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full)
+static inline bool
+rb_wait_cond(struct rb_irq_work *rbwork, struct trace_buffer *buffer,
+	     int cpu, int full, ring_buffer_cond_fn cond, void *data)
 {
-	struct ring_buffer_per_cpu *cpu_buffer;
-	DEFINE_WAIT(wait);
-	struct rb_irq_work *work;
-	int ret = 0;
-
-	/*
-	 * Depending on what the caller is waiting for, either any
-	 * data in any cpu buffer, or a specific buffer, put the
-	 * caller on the appropriate wait queue.
-	 */
-	if (cpu == RING_BUFFER_ALL_CPUS) {
-		work = &buffer->irq_work;
-		/* Full only makes sense on per cpu reads */
-		full = 0;
-	} else {
-		if (!cpumask_test_cpu(cpu, buffer->cpumask))
-			return -ENODEV;
-		cpu_buffer = buffer->buffers[cpu];
-		work = &cpu_buffer->irq_work;
-	}
+	if (rb_watermark_hit(buffer, cpu, full))
+		return true;
 
-	if (full)
-		prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
-	else
-		prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
+	if (cond(data))
+		return true;
 
 	/*
 	 * The events can happen in critical sections where
@@ -901,27 +874,78 @@ int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full)
 	 * a task has been queued. It's OK for spurious wake ups.
 	 */
 	if (full)
-		work->full_waiters_pending = true;
+		rbwork->full_waiters_pending = true;
 	else
-		work->waiters_pending = true;
+		rbwork->waiters_pending = true;
 
-	if (rb_watermark_hit(buffer, cpu, full))
-		goto out;
+	return false;
+}
 
-	if (signal_pending(current)) {
-		ret = -EINTR;
-		goto out;
+/*
+ * The default wait condition for ring_buffer_wait() is to just to exit the
+ * wait loop the first time it is woken up.
+ */
+static bool rb_wait_once(void *data)
+{
+	long *once = data;
+
+	/* wait_event() actually calls this twice before scheduling*/
+	if (*once > 1)
+		return true;
+
+	(*once)++;
+	return false;
+}
+
+/**
+ * ring_buffer_wait - wait for input to the ring buffer
+ * @buffer: buffer to wait on
+ * @cpu: the cpu buffer to wait on
+ * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
+ * @cond: condition function to break out of wait (NULL to run once)
+ * @data: the data to pass to @cond.
+ *
+ * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
+ * as data is added to any of the @buffer's cpu buffers. Otherwise
+ * it will wait for data to be added to a specific cpu buffer.
+ */
+int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full,
+		     ring_buffer_cond_fn cond, void *data)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct wait_queue_head *waitq;
+	struct rb_irq_work *rbwork;
+	long once = 0;
+	int ret = 0;
+
+	if (!cond) {
+		cond = rb_wait_once;
+		data = &once;
+	}
+
+	/*
+	 * Depending on what the caller is waiting for, either any
+	 * data in any cpu buffer, or a specific buffer, put the
+	 * caller on the appropriate wait queue.
+	 */
+	if (cpu == RING_BUFFER_ALL_CPUS) {
+		rbwork = &buffer->irq_work;
+		/* Full only makes sense on per cpu reads */
+		full = 0;
+	} else {
+		if (!cpumask_test_cpu(cpu, buffer->cpumask))
+			return -ENODEV;
+		cpu_buffer = buffer->buffers[cpu];
+		rbwork = &cpu_buffer->irq_work;
 	}
 
-	schedule();
- out:
 	if (full)
-		finish_wait(&work->full_waiters, &wait);
+		waitq = &rbwork->full_waiters;
 	else
-		finish_wait(&work->waiters, &wait);
+		waitq = &rbwork->waiters;
 
-	if (!ret && !rb_watermark_hit(buffer, cpu, full) && signal_pending(current))
-		ret = -EINTR;
+	ret = wait_event_interruptible((*waitq),
+				rb_wait_cond(rbwork, buffer, cpu, full, cond, data));
 
 	return ret;
 }
@@ -959,21 +983,30 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
 	}
 
 	if (full) {
-		unsigned long flags;
-
 		poll_wait(filp, &rbwork->full_waiters, poll_table);
 
-		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+		if (rb_watermark_hit(buffer, cpu, full))
+			return EPOLLIN | EPOLLRDNORM;
+		/*
+		 * Only allow full_waiters_pending update to be seen after
+		 * the shortest_full is set (in rb_watermark_hit). If the
+		 * writer sees the full_waiters_pending flag set, it will
+		 * compare the amount in the ring buffer to shortest_full.
+		 * If the amount in the ring buffer is greater than the
+		 * shortest_full percent, it will call the irq_work handler
+		 * to wake up this list. The irq_handler will reset shortest_full
+		 * back to zero. That's done under the reader_lock, but
+		 * the below smp_mb() makes sure that the update to
+		 * full_waiters_pending doesn't leak up into the above.
+		 */
+		smp_mb();
 		rbwork->full_waiters_pending = true;
-		if (!cpu_buffer->shortest_full ||
-		    cpu_buffer->shortest_full > full)
-			cpu_buffer->shortest_full = full;
-		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
-	} else {
-		poll_wait(filp, &rbwork->waiters, poll_table);
-		rbwork->waiters_pending = true;
+		return 0;
 	}
 
+	poll_wait(filp, &rbwork->waiters, poll_table);
+	rbwork->waiters_pending = true;
+
 	/*
 	 * There's a tight race between setting the waiters_pending and
 	 * checking if the ring buffer is empty.  Once the waiters_pending bit
@@ -989,9 +1022,6 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
 	 */
 	smp_mb();
 
-	if (full)
-		return full_hit(buffer, cpu, full) ? EPOLLIN | EPOLLRDNORM : 0;
-
 	if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
 	    (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
 		return EPOLLIN | EPOLLRDNORM;