[PATCH 6.0 199/314] ring_buffer: Do not deactivate non-existant pages

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From: Daniil Tatianin <d-tatianin@xxxxxxxxxxxxxx>

commit 56f4ca0a79a9f1af98f26c54b9b89ba1f9bcc6bd upstream.

rb_head_page_deactivate() expects cpu_buffer to contain a valid list of
->pages, so verify that the list is actually present before calling it.

Found by Linux Verification Center (linuxtesting.org) with the SVACE
static analysis tool.

Link: https://lkml.kernel.org/r/20221114143129.3534443-1-d-tatianin@xxxxxxxxxxxxxx

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 77ae365eca895 ("ring-buffer: make lockless")
Signed-off-by: Daniil Tatianin <d-tatianin@xxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/trace/ring_buffer.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1769,9 +1769,9 @@ static void rb_free_cpu_buffer(struct ri
 
 	free_buffer_page(cpu_buffer->reader_page);
 
-	rb_head_page_deactivate(cpu_buffer);
-
 	if (head) {
+		rb_head_page_deactivate(cpu_buffer);
+
 		list_for_each_entry_safe(bpage, tmp, head, list) {
 			list_del_init(&bpage->list);
 			free_buffer_page(bpage);





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