Merge tag 'trace-ringbuffer-v6.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull ring-buffer fixes from Steven Rostedt:

- Fix ref counter of buffers assigned at boot up

A tracing instance can be created from the kernel command line. If it
maps to memory, it is considered permanent and should not be deleted,
or bad things can happen. If it is not mapped to memory, then the
user is fine to delete it via rmdir from the instances directory. But
the ref counts assumed 0 was free to remove and greater than zero was
not. But this was not the case. When an instance is created, it
should have the reference of 1, and if it should not be removed, it
must be greater than 1. The boot up code set normal instances with a
ref count of 0, which could get removed if something accessed it and
then released it. And memory mapped instances had a ref count of 1
which meant it could be deleted, and bad things happen. Keep normal
instances ref count as 1, and set memory mapped instances ref count
to 2.

- Protect sub buffer size (order) updates from other modifications

When a ring buffer is changing the size of its sub-buffers, no other
operations should be performed on the ring buffer. That includes
reading it. But the locking only grabbed the buffer->mutex that keeps
some operations from touching the ring buffer. It also must hold the
cpu_buffer->reader_lock as well when updates happen as other paths
use that to do some operations on the ring buffer.

* tag 'trace-ringbuffer-v6.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
ring-buffer: Fix reader locking when changing the sub buffer order
ring-buffer: Fix refcount setting of boot mapped buffers

kernel/trace/ring_buffer.c

···
 	}
 
 	for_each_buffer_cpu(buffer, cpu) {
+		struct buffer_data_page *old_free_data_page;
+		struct list_head old_pages;
+		unsigned long flags;
 
 		if (!cpumask_test_cpu(cpu, buffer->cpumask))
 			continue;
 
 		cpu_buffer = buffer->buffers[cpu];
 
+		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
 		/* Clear the head bit to make the link list normal to read */
 		rb_head_page_deactivate(cpu_buffer);
 
-		/* Now walk the list and free all the old sub buffers */
-		list_for_each_entry_safe(bpage, tmp, cpu_buffer->pages, list) {
-			list_del_init(&bpage->list);
-			free_buffer_page(bpage);
-		}
-		/* The above loop stopped an the last page needing to be freed */
-		bpage = list_entry(cpu_buffer->pages, struct buffer_page, list);
-		free_buffer_page(bpage);
-
-		/* Free the current reader page */
-		free_buffer_page(cpu_buffer->reader_page);
+		/*
+		 * Collect buffers from the cpu_buffer pages list and the
+		 * reader_page on old_pages, so they can be freed later when not
+		 * under a spinlock. The pages list is a linked list with no
+		 * head, adding old_pages turns it into a regular list with
+		 * old_pages being the head.
+		 */
+		list_add(&old_pages, cpu_buffer->pages);
+		list_add(&cpu_buffer->reader_page->list, &old_pages);
 
 		/* One page was allocated for the reader page */
 		cpu_buffer->reader_page = list_entry(cpu_buffer->new_pages.next,
 						     struct buffer_page, list);
 		list_del_init(&cpu_buffer->reader_page->list);
 
-		/* The cpu_buffer pages are a link list with no head */
+		/* Install the new pages, remove the head from the list */
 		cpu_buffer->pages = cpu_buffer->new_pages.next;
-		cpu_buffer->new_pages.next->prev = cpu_buffer->new_pages.prev;
-		cpu_buffer->new_pages.prev->next = cpu_buffer->new_pages.next;
-
-		/* Clear the new_pages list */
-		INIT_LIST_HEAD(&cpu_buffer->new_pages);
+		list_del_init(&cpu_buffer->new_pages);
 
 		cpu_buffer->head_page
 			= list_entry(cpu_buffer->pages, struct buffer_page, list);
···
 		cpu_buffer->nr_pages = cpu_buffer->nr_pages_to_update;
 		cpu_buffer->nr_pages_to_update = 0;
 
-		free_pages((unsigned long)cpu_buffer->free_page, old_order);
+		old_free_data_page = cpu_buffer->free_page;
 		cpu_buffer->free_page = NULL;
 
 		rb_head_page_activate(cpu_buffer);
+
+		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+		/* Free old sub buffers */
+		list_for_each_entry_safe(bpage, tmp, &old_pages, list) {
+			list_del_init(&bpage->list);
+			free_buffer_page(bpage);
+		}
+		free_pages((unsigned long)old_free_data_page, old_order);
 
 		rb_check_pages(cpu_buffer);
 	}

kernel/trace/trace.c

···
 		 * cannot be deleted by user space, so keep the reference
 		 * to it.
 		 */
-		if (start)
+		if (start) {
 			tr->flags |= TRACE_ARRAY_FL_BOOT;
-		else
-			trace_array_put(tr);
+			tr->ref++;
+		}
 
 		while ((tok = strsep(&curr_str, ","))) {
 			early_enable_events(tr, tok, true);