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

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Date:	Wed, 9 Apr 2008 15:35:17 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Johannes Weiner <hannes@...urebad.de>
cc:	Roel Kluin <12o3l@...cali.nl>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dz: test after postfix decrement fails in
 dz_console_putchar()

On Wed, 9 Apr 2008, Johannes Weiner wrote:

> 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.

 You are right about the intention -- you cannot send a character to the 
transmitter unless the intended line has been reported as selected for 
transmission by the serial controller.  Otherwise it will go to the wrong 
line -- this is a serial multiplexer that selects transmission lines by 
itself.

 It used to be the other kind of a "while" loop.  This is a cut & paste 
bug -- I noticed the problem with the terminating condition of the loop 
and correctly moved it to the end, but forgot to adjust the 
decrementation.

> Your fix is correct but your changelog entry is wrong.

 s/fails/incorrectly succeeds/

  Maciej
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