ring_buffer: Do not deactivate non-existant pages

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@yandex-team.ru
Cc: stable@vger.kernel.org
Fixes: 77ae365eca895 ("ring-buffer: make lockless")
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a19369c..b21bf14 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1802,9 +1802,9 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 
        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);