ring-buffer: Clearly check null ptr returned by rb_set_head_page()

In error case, 'buffer_page' returned by rb_set_head_page() is NULL,
currently check '&buffer_page->list' is equivalent to check 'buffer_page'
due to 'list' is the first member of 'buffer_page', but suppose it is not
some time, 'head_page' would be wild memory while check would be bypassed.

Link: https://lore.kernel.org/linux-trace-kernel/20230414071729.57312-1-zhengyejian1@huawei.com
Cc: <mhiramat@kernel.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2d5c3caff32d72a5d14908877285be58954b9b68..58be5b409f72f7b712464b1efab0a175f2373500 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2054,10 +2054,11 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
                struct list_head *head_page, *prev_page, *r;
                struct list_head *last_page, *first_page;
                struct list_head *head_page_with_bit;
+               struct buffer_page *hpage = rb_set_head_page(cpu_buffer);
 
-               head_page = &rb_set_head_page(cpu_buffer)->list;
-               if (!head_page)
+               if (!hpage)
                        break;
+               head_page = &hpage->list;
                prev_page = head_page->prev;
 
                first_page = pages->next;