Merge tag 'trace-ring-buffer-v6.8-rc7-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing updates from Steven Rostedt:

 - Do not update shortest_full in rb_watermark_hit() if the watermark is
   hit. The shortest_full field was being updated regardless if the task
   was going to wait or not. If the watermark is hit, then the task is
   not going to wait, so do not update the shortest_full field (used by
   the waker).

 - Update shortest_full field before setting the full_waiters_pending
   flag

   In the poll logic, the full_waiters_pending flag was being set before
   the shortest_full field was set. If the full_waiters_pending flag is
   set, writers will check the shortest_full field which has the least
   percentage of data that the ring buffer needs to be filled before
   waking up. The writer will check shortest_full if
   full_waiters_pending is set, and if the ring buffer percentage filled
   is greater than shortest full, then it will call the irq_work to wake
   up the waiters.

   The problem was that the poll logic set the full_waiters_pending flag
   before updating shortest_full, which when zero will always trigger
   the writer to call the irq_work to wake up the waiters. The irq_work
   will reset the shortest_full field back to zero as the woken waiters
   is suppose to reset it.

 - There's some optimized logic in the rb_watermark_hit() that is used
   in ring_buffer_wait(). Use that helper function in the poll logic as
   well.

 - Restructure ring_buffer_wait() to use wait_event_interruptible()

   The logic to wake up pending readers when the file descriptor is
   closed is racy. Restructure ring_buffer_wait() to allow callers to
   pass in conditions besides the ring buffer having enough data in it
   by using wait_event_interruptible().

 - Update the tracing_wait_on_pipe() to call ring_buffer_wait() with its
   own conditions to exit the wait loop.

* tag 'trace-ring-buffer-v6.8-rc7-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  tracing/ring-buffer: Fix wait_on_pipe() race
  ring-buffer: Use wait_event_interruptible() in ring_buffer_wait()
  ring-buffer: Reuse rb_watermark_hit() for the poll logic
  ring-buffer: Fix full_waiters_pending in poll
  ring-buffer: Do not set shortest_full when full target is hit

2 files changed, 7 insertions, 2 deletions

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index fa802db216f9..dc5ae4e96aee 100644
--- a/include/linux/ring_buffer.h
+++ b/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);
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index d68ff9b1247f..fc6d0af56bb1 100644
--- a/include/linux/trace_events.h
+++ b/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;