Merge tag 'trace-v6.2-rc7-3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing fix from Steven Rostedt:
"Fix race that causes a warning of corrupt ring buffer

With the change that allows to read the "trace" file without disabling
writing to the ring buffer, there was an integrity check of the ring
buffer in the iterator read code, that expected the ring buffer to be
write disabled. This caused the integrity check to trigger when stress
reading the "trace" file while writing was happening.

The integrity check is a bit aggressive (and has never triggered in
practice). Change it so that it checks just the integrity of the
linked pages without clearing the flags inside the pointers. This
removes the warning that was being triggered"

[ Heh. This was supposed to have gone in last week before the 6.2
release, but Steven forgot to actually add me to the participants of
the pull request, so here it is, a week later - Linus ]

* tag 'trace-v6.2-rc7-3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
ring-buffer: Handle race between rb_move_tail and rb_check_pages

kernel/trace/ring_buffer.c

···
 }
 
 /**
- * rb_check_list - make sure a pointer to a list has the last bits zero
- */
-static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
-			 struct list_head *list)
-{
-	if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
-		return 1;
-	if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
-		return 1;
-	return 0;
-}
-
-/**
  * rb_check_pages - integrity check of buffer pages
  * @cpu_buffer: CPU buffer with pages to test
  *
···
  */
 static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
 {
-	struct list_head *head = cpu_buffer->pages;
-	struct buffer_page *bpage, *tmp;
+	struct list_head *head = rb_list_head(cpu_buffer->pages);
+	struct list_head *tmp;
 
-	/* Reset the head page if it exists */
-	if (cpu_buffer->head_page)
-		rb_set_head_page(cpu_buffer);
-
-	rb_head_page_deactivate(cpu_buffer);
-
-	if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
-		return -1;
-	if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
+	if (RB_WARN_ON(cpu_buffer,
+			rb_list_head(rb_list_head(head->next)->prev) != head))
 		return -1;
 
-	if (rb_check_list(cpu_buffer, head))
+	if (RB_WARN_ON(cpu_buffer,
+			rb_list_head(rb_list_head(head->prev)->next) != head))
 		return -1;
 
-	list_for_each_entry_safe(bpage, tmp, head, list) {
+	for (tmp = rb_list_head(head->next); tmp != head; tmp = rb_list_head(tmp->next)) {
 		if (RB_WARN_ON(cpu_buffer,
-			       bpage->list.next->prev != &bpage->list))
+				rb_list_head(rb_list_head(tmp->next)->prev) != tmp))
 			return -1;
+
 		if (RB_WARN_ON(cpu_buffer,
-			       bpage->list.prev->next != &bpage->list))
-			return -1;
-		if (rb_check_list(cpu_buffer, &bpage->list))
+				rb_list_head(rb_list_head(tmp->prev)->next) != tmp))
 			return -1;
 	}
-
-	rb_head_page_activate(cpu_buffer);
 
 	return 0;
 }