This is a note to let you know that I've just added the patch titled
ring-buffer: Fix reader locking when changing the sub buffer order
to the 6.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ring-buffer-fix-reader-locking-when-changing-the-sub.patch
and it can be found in the queue-6.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 5124906a55e88bea64d0d818560c459dddec839c
Author: Petr Pavlu <petr.pavlu@xxxxxxxx>
Date: Tue Oct 15 13:24:29 2024 +0200
ring-buffer: Fix reader locking when changing the sub buffer order
[ Upstream commit 09661f75e75cb6c1d2d8326a70c311d46729235f ]
The function ring_buffer_subbuf_order_set() updates each
ring_buffer_per_cpu and installs new sub buffers that match the requested
page order. This operation may be invoked concurrently with readers that
rely on some of the modified data, such as the head bit (RB_PAGE_HEAD), or
the ring_buffer_per_cpu.pages and reader_page pointers. However, no
exclusive access is acquired by ring_buffer_subbuf_order_set(). Modifying
the mentioned data while a reader also operates on them can then result in
incorrect memory access and various crashes.
Fix the problem by taking the reader_lock when updating a specific
ring_buffer_per_cpu in ring_buffer_subbuf_order_set().
Link: https://lore.kernel.org/linux-trace-kernel/20240715145141.5528-1-petr.pavlu@xxxxxxxx/
Link: https://lore.kernel.org/linux-trace-kernel/20241010195849.2f77cc3f@xxxxxxxxxxxxxxxxxx/
Link: https://lore.kernel.org/linux-trace-kernel/20241011112850.17212b25@xxxxxxxxxxxxxxxxxx/
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Link: https://lore.kernel.org/20241015112440.26987-1-petr.pavlu@xxxxxxxx
Fixes: 8e7b58c27b3c ("ring-buffer: Just update the subbuffers when changing their allocation order")
Signed-off-by: Petr Pavlu <petr.pavlu@xxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index cebd879a30cbd..fb7b092e79313 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6008,39 +6008,38 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
}
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);
@@ -6049,11 +6048,20 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
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);
}
