kernel/panic.c: taint: fix debugfs_simple_attr.cocci warnings

Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE for
debugfs files.

Semantic patch information:
Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
imposes some significant overhead as compared to
DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().

Generated by: scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci

The _unsafe() part suggests that some of them "safeness
responsibilities" are now panic.c responsibilities.  The patch is OK
since panic's clear_warn_once_fops struct file_operations is safe
against removal, so we don't have to use otherwise necessary
debugfs_file_get()/debugfs_file_put().

[sergey.senozhatsky.work@gmail.com: changelog addition]
Link: http://lkml.kernel.org/r/1545990861-158097-1-git-send-email-yuehaibing@huawei.comSigned-off-by: NYueHaibing <yuehaibing@huawei.com>
Reviewed-by: NSergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/panic.c

@@ -642,16 +642,14 @@ static int clear_warn_once_set(void *data, u64 val)
 	return 0;
 }
 
-DEFINE_SIMPLE_ATTRIBUTE(clear_warn_once_fops,
-			NULL,
-			clear_warn_once_set,
+DEFINE_DEBUGFS_ATTRIBUTE(clear_warn_once_fops, NULL, clear_warn_once_set,
 			 "%lld\n");
 
 static __init int register_warn_debugfs(void)
 {
 	/* Don't care about failure */
-	debugfs_create_file("clear_warn_once", 0200, NULL,
-			    NULL, &clear_warn_once_fops);
+	debugfs_create_file_unsafe("clear_warn_once", 0200, NULL, NULL,
+				   &clear_warn_once_fops);
 	return 0;
 }