x86: Mark __invalid_creds() __noreturn

vmlinux.o: warning: objtool: ksys_unshare()+0x36c: unreachable instruction

0000 0000000000067040 <ksys_unshare>:
...
0364    673a4:	4c 89 ef             	mov    %r13,%rdi
0367    673a7:	e8 00 00 00 00       	call   673ac <ksys_unshare+0x36c>	673a8: R_X86_64_PLT32	__invalid_creds-0x4
036c    673ac:	e9 28 ff ff ff       	jmp    672d9 <ksys_unshare+0x299>
0371    673b1:	41 bc f4 ff ff ff    	mov    $0xfffffff4,%r12d
0377    673b7:	e9 80 fd ff ff       	jmp    6713c <ksys_unshare+0xfc>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/Yi9gOW9f1GGwwUD6@hirez.programming.kicks-ass.net

include/linux/cred.h

@@ -176,7 +176,7 @@ extern int set_cred_ucounts(struct cred *);
  * check for validity of credentials
  */
 #ifdef CONFIG_DEBUG_CREDENTIALS
-extern void __invalid_creds(const struct cred *, const char *, unsigned);
+extern void __noreturn __invalid_creds(const struct cred *, const char *, unsigned);
 extern void __validate_process_creds(struct task_struct *,
 				     const char *, unsigned);
 

kernel/cred.c

@@ -870,7 +870,7 @@ static void dump_invalid_creds(const struct cred *cred, const char *label,
 /*
  * report use of invalid credentials
  */
-void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
+void __noreturn __invalid_creds(const struct cred *cred, const char *file, unsigned line)
 {
 	printk(KERN_ERR "CRED: Invalid credentials\n");
 	printk(KERN_ERR "CRED: At %s:%u\n", file, line);

tools/objtool/check.c

@@ -183,6 +183,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"cpu_bringup_and_idle",
 		"do_group_exit",
 		"stop_this_cpu",
+		"__invalid_creds",
 	};
 
 	if (!func)