Merge 63bd30f249 ("Merge tag 'trace-ring-buffer-v6.8-rc7-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace") into android-mainline

Steps on the way to v6.9-rc1

Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: Ibb929cd0f27994ce4775d685dee6a4bd71bb06e9

include/linux/ring_buffer.h

@@ -98,7 +98,9 @@ __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *k
 	__ring_buffer_alloc((size), (flags), &__key);	\
 })
 
-int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full);
+typedef bool (*ring_buffer_cond_fn)(void *data);
+int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full,
+		     ring_buffer_cond_fn cond, void *data);
 __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
 			  struct file *filp, poll_table *poll_table, int full);
 void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu);

include/linux/trace_events.h

@@ -103,13 +103,16 @@ struct trace_iterator {
 	unsigned int		temp_size;
 	char			*fmt;	/* modified format holder */
 	unsigned int		fmt_size;
-	long			wait_index;
+	atomic_t		wait_index;
 
 	/* trace_seq for __print_flags() and __print_symbolic() etc. */
 	struct trace_seq	tmp_seq;
 
 	cpumask_var_t		started;
 
+	/* Set when the file is closed to prevent new waiters */
+	bool			closed;
+
 	/* it's true when current open file is snapshot */
 	bool			snapshot;
 

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;
+	if (rb_watermark_hit(buffer, cpu, full))
+		return true;
 
-	/*
-	 * 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 (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;
 	}
 
-	schedule();
- out:
-	if (full)
-		finish_wait(&work->full_waiters, &wait);
-	else
-		finish_wait(&work->waiters, &wait);
+	/*
+	 * 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;
+	}
 
-	if (!ret && !rb_watermark_hit(buffer, cpu, full) && signal_pending(current))
-		ret = -EINTR;
+	if (full)
+		waitq = &rbwork->full_waiters;
+	else
+		waitq = &rbwork->waiters;
+
+	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;

kernel/trace/trace.c

@@ -1955,15 +1955,36 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
 
 #endif /* CONFIG_TRACER_MAX_TRACE */
 
+struct pipe_wait {
+	struct trace_iterator		*iter;
+	int				wait_index;
+};
+
+static bool wait_pipe_cond(void *data)
+{
+	struct pipe_wait *pwait = data;
+	struct trace_iterator *iter = pwait->iter;
+
+	if (atomic_read_acquire(&iter->wait_index) != pwait->wait_index)
+		return true;
+
+	return iter->closed;
+}
+
 static int wait_on_pipe(struct trace_iterator *iter, int full)
 {
+	struct pipe_wait pwait;
 	int ret;
 
 	/* Iterators are static, they should be filled or empty */
 	if (trace_buffer_iter(iter, iter->cpu_file))
 		return 0;
 
-	ret = ring_buffer_wait(iter->array_buffer->buffer, iter->cpu_file, full);
+	pwait.wait_index = atomic_read_acquire(&iter->wait_index);
+	pwait.iter = iter;
+
+	ret = ring_buffer_wait(iter->array_buffer->buffer, iter->cpu_file, full,
+			       wait_pipe_cond, &pwait);
 
 #ifdef CONFIG_TRACER_MAX_TRACE
 	/*
@@ -8397,9 +8418,9 @@ static int tracing_buffers_flush(struct file *file, fl_owner_t id)
 	struct ftrace_buffer_info *info = file->private_data;
 	struct trace_iterator *iter = &info->iter;
 
-	iter->wait_index++;
+	iter->closed = true;
 	/* Make sure the waiters see the new wait_index */
-	smp_wmb();
+	(void)atomic_fetch_inc_release(&iter->wait_index);
 
 	ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);
 
@@ -8499,6 +8520,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 		.spd_release	= buffer_spd_release,
 	};
 	struct buffer_ref *ref;
+	bool woken = false;
 	int page_size;
 	int entries, i;
 	ssize_t ret = 0;
@@ -8572,17 +8594,17 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 
 	/* did we read anything? */
 	if (!spd.nr_pages) {
-		long wait_index;
 
 		if (ret)
 			goto out;
 
+		if (woken)
+			goto out;
+
 		ret = -EAGAIN;
 		if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))
 			goto out;
 
-		wait_index = READ_ONCE(iter->wait_index);
-
 		ret = wait_on_pipe(iter, iter->snapshot ? 0 : iter->tr->buffer_percent);
 		if (ret)
 			goto out;
@@ -8591,10 +8613,8 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 		if (!tracer_tracing_is_on(iter->tr))
 			goto out;
 
-		/* Make sure we see the new wait_index */
-		smp_rmb();
-		if (wait_index != iter->wait_index)
-			goto out;
+		/* Iterate one more time to collect any new data then exit */
+		woken = true;
 
 		goto again;
 	}
@@ -8617,9 +8637,8 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned
 
 	mutex_lock(&trace_types_lock);
 
-	iter->wait_index++;
 	/* Make sure the waiters see the new wait_index */
-	smp_wmb();
+	(void)atomic_fetch_inc_release(&iter->wait_index);
 
 	ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);