Don't acquire filesys lock when calling exec

src/userprog/syscall.c

@@ -142,9 +142,7 @@ syscall_exec (const char *cmd_line)
 {
   validate_user_pointer (cmd_line, 1);
 
-  lock_acquire (&filesys_lock);
   pid_t pid = process_execute(cmd_line);
-  lock_release (&filesys_lock);
 
   return pid;
 }