Dump stack during sysctl registration failure

Let's make immediately obvious from where sysctl comes from and messages
itself more noticeable.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sysctl_check.c

@@ -1432,6 +1432,7 @@ static void set_fail(const char **fail, struct ctl_table *table, const char *str
 		printk(KERN_ERR "sysctl table check failed: ");
 		sysctl_print_path(table);
 		printk(" %s\n", *fail);
+		dump_stack();
 	}
 	*fail = str;
 }