linux-kernel - Re: [PATCH] dz: test after postfix decrement fails in dz_console

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Message-ID: <87ve2rqh6u.fsf@saeurebad.de>
Date:	Wed, 09 Apr 2008 15:41:13 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Roel Kluin <12o3l@...cali.nl>
Cc:	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dz: test after postfix decrement fails in dz_console_putchar()

Hi,

Roel Kluin <12o3l@...cali.nl> writes:

> When loops reaches 0 the postfix decrement still subtracts, so the test fails
>
> Signed-off-by: Roel Kluin <12o3l@...cali.nl>
> ---
> diff --git a/drivers/serial/dz.c b/drivers/serial/dz.c
> index 116211f..0dddd68 100644
> --- a/drivers/serial/dz.c
> +++ b/drivers/serial/dz.c
> @@ -819,7 +819,7 @@ static void dz_console_putchar(struct uart_port *uport, int ch)
>  		dz_out(dport, DZ_TCR, mask);
>  		iob();
>  		udelay(2);
> -	} while (loops--);
> +	} while (--loops);

It will run loops + 1 times.  After your change it does run loops times.

>  	if (loops)				/* Cannot send otherwise. */
>  		dz_out(dport, DZ_TDR, ch);

The intention was probably that this gets executed if the break in the
loop (trdy == dport->port.line) is reached.  Without your fix, this
branch is also taken if the while-loop terminates with loops == -1
because of the postfix dec.

Your fix is correct but your changelog entry is wrong.

	Hannes
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