arm64: Remove unimplemented syscall log message

commit 1962682 upstream.

Stop printing a (ratelimited) kernel message for each instance of an
unimplemented syscall being called. Userland making an unimplemented
syscall is not necessarily misbehaviour and to be expected with a
current userland running on an older kernel. Also, the current message
looks scary to users but does not actually indicate a real problem nor
help them narrow down the cause. Just rely on sys_ni_syscall() to return
-ENOSYS.

Cc: <[email protected]>
Acked-by: Will Deacon <[email protected]>
Signed-off-by: Michael Weiser <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

arch/arm64/kernel/traps.c

@@ -573,14 +573,6 @@ asmlinkage long do_ni_syscall(struct pt_regs *regs)
 	}
 #endif
 
-	if (show_unhandled_signals_ratelimited()) {
-		pr_info("%s[%d]: syscall %d\n", current->comm,
-			task_pid_nr(current), regs->syscallno);
-		dump_instr("", regs);
-		if (user_mode(regs))
-			__show_regs(regs);
-	}
-
 	return sys_ni_syscall();
 }