linux-kernel - Re: [PATCH v2 5/6] hpet: removing unused variable m in hpet

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Message-ID: <64bd824c-2d09-3c8c-d35d-06d3808713b2@ladisch.de>
Date:   Mon, 3 Apr 2017 14:55:14 +0200
From:   Clemens Ladisch <clemens@...isch.de>
To:     Corentin Labbe <clabbe.montjoie@...il.com>, arnd@...db.de
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] hpet: removing unused variable m in hpet_interrupt

Corentin Labbe wrote:
> This patch fix the following warning:
> drivers/char/hpet.c:146:17: attention : variable ‘m’ set but not used [-Wunused-but-set-variable]
> by removing the unused variable m in hpet_interrupt

This patch might silence the warning, but it leaves the bug that
actually caused the warning.

As far as I can see, the computation of "base" should use "m".

But the entire algorithm is completely bogus because it does not
actually remove the race condition; the counter is likely to have
advanced beyond the "mc" value when the new comparator value is
written.  Also see arch/x86/kernel/hpet.c for how hpet_next_event()
handles this.

And why a non-periodic timer should generate periodic interrupts is
another question.

And nobody uses this crap.
So I'm really not sure what to do about this ...

Regards,
Clemens