Reapply "ANDROID: Revert "tracing/ring-buffer: Have polling block on watermark""

This reverts commit 541686ad47d2b3eb58a3d809322fe558b3b2c948, which
reapplys the original revert as the original is still causing crashes.

Bug: 263508491
Cc: Lee Jones <joneslee@google.com>
Change-Id: I35cd4d9cef24e64f2dc3afad85d90d588c09e5f0
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

include/linux/ring_buffer.h

@@ -99,7 +99,7 @@ __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *k
 
 int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full);
 __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
-			  struct file *filp, poll_table *poll_table, int full);
+			  struct file *filp, poll_table *poll_table);
 
 
 #define RING_BUFFER_ALL_CPUS -1

kernel/trace/ring_buffer.c

@@ -569,21 +569,6 @@ size_t ring_buffer_nr_dirty_pages(struct ring_buffer *buffer, int cpu)
 	return cnt - read;
 }
 
-static __always_inline bool full_hit(struct ring_buffer *buffer, int cpu, int full)
-{
-	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
-	size_t nr_pages;
-	size_t dirty;
-
-	nr_pages = cpu_buffer->nr_pages;
-	if (!nr_pages || !full)
-		return true;
-
-	dirty = ring_buffer_nr_dirty_pages(buffer, cpu);
-
-	return (dirty * 100) > (full * nr_pages);
-}
-
 /*
  * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
  *
@@ -679,20 +664,22 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full)
 		    !ring_buffer_empty_cpu(buffer, cpu)) {
 			unsigned long flags;
 			bool pagebusy;
-			bool done;
+			size_t nr_pages;
+			size_t dirty;
 
 			if (!full)
 				break;
 
 			raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 			pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
-			done = !pagebusy && full_hit(buffer, cpu, full);
+			nr_pages = cpu_buffer->nr_pages;
-
+			dirty = ring_buffer_nr_dirty_pages(buffer, cpu);
 			if (!cpu_buffer->shortest_full ||
 			    cpu_buffer->shortest_full > full)
 				cpu_buffer->shortest_full = full;
 			raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
-			if (done)
+			if (!pagebusy &&
+			    (!nr_pages || (dirty * 100) > full * nr_pages))
 				break;
 		}
 
@@ -713,7 +700,6 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full)
  * @cpu: the cpu buffer to wait on
  * @filp: the file descriptor
  * @poll_table: The poll descriptor
- * @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
@@ -723,14 +709,14 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full)
  * zero otherwise.
  */
 __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
-			  struct file *filp, poll_table *poll_table, int full)
+			  struct file *filp, poll_table *poll_table)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct rb_irq_work *work;
 
-	if (cpu == RING_BUFFER_ALL_CPUS) {
+	if (cpu == RING_BUFFER_ALL_CPUS)
 		work = &buffer->irq_work;
-	} else {
+	else {
 		if (!cpumask_test_cpu(cpu, buffer->cpumask))
 			return -EINVAL;
 
@@ -738,14 +724,8 @@ __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
 		work = &cpu_buffer->irq_work;
 	}
 
-	if (full) {
+	poll_wait(filp, &work->waiters, poll_table);
-		poll_wait(filp, &work->full_waiters, poll_table);
+	work->waiters_pending = true;
-		work->full_waiters_pending = true;
-	} else {
-		poll_wait(filp, &work->waiters, poll_table);
-		work->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
@@ -761,9 +741,6 @@ __poll_t ring_buffer_poll_wait(struct ring_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;
@@ -2674,6 +2651,10 @@ static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
 static __always_inline void
 rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
 {
+	size_t nr_pages;
+	size_t dirty;
+	size_t full;
+
 	if (buffer->irq_work.waiters_pending) {
 		buffer->irq_work.waiters_pending = false;
 		/* irq_work_queue() supplies it's own memory barriers */
@@ -2697,7 +2678,10 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
 
 	cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
 
-	if (!full_hit(buffer, cpu_buffer->cpu, cpu_buffer->shortest_full))
+	full = cpu_buffer->shortest_full;
+	nr_pages = cpu_buffer->nr_pages;
+	dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu);
+	if (full && nr_pages && (dirty * 100) <= full * nr_pages)
 		return;
 
 	cpu_buffer->irq_work.wakeup_full = true;

kernel/trace/trace.c

@@ -6036,7 +6036,7 @@ trace_poll(struct trace_iterator *iter, struct file *filp, poll_table *poll_tabl
 		return EPOLLIN | EPOLLRDNORM;
 	else
 		return ring_buffer_poll_wait(iter->trace_buffer->buffer, iter->cpu_file,
-					     filp, poll_table, iter->tr->buffer_percent);
+					     filp, poll_table);
 }
 
 static __poll_t