linux-kernel - Re: Wireless IBSS on Linux-2.6.34 broken by commit 3bbb9ec946428b96657126768f65487a48dd090c

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Message-ID: <Pine.LNX.4.64.1005250637530.3140@boston.corp.fedex.com>
Date:	Tue, 25 May 2010 06:48:35 +0800 (SGT)
From:	Jeff Chua <jeff.chua.linux@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Johannes Berg <johannes.berg@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"johnstul@...ibm.com" <johnstul@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Intel Linux Wireless <ilw@...ux.intel.com>,
	"John W. Linville" <linville@...driver.com>,
	Frans Pop <elendil@...net.nl>,
	"Chatre, Reinette" <reinette.chatre@...el.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: Wireless IBSS on Linux-2.6.34 broken by commit
 3bbb9ec946428b96657126768f65487a48dd090c



On Mon, May 24, 2010 at 10:57 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:>
> On Mon, 24 May 2010, Jeff Chua wrote:
>> +     if (timer->slack > -1)
>> +     else if (time_after(expires, jiffies)) /* auto slack: use 0.4% */
>>               expires_limit = expires + (expires - jiffies)/256;
>
> Please don't reload 'jiffies' twice. It's volatile, and the compiler will
> do a crap job of it.

Linus,

Sorry, didn't know what a jiffies was before, so didn't know about the 
crap it caused. Now I learned something new.

> Also, '0' is a normal number, but '-1' is a rather odd value. Please just
> test for non-negative by doing ">= 0" rather than "> -1"

Fixed.

Below is the patch to fix jiffies and checking for non-negative.


Thanks,
Jeff

--- a/kernel/timer.c.org	2010-05-25 06:05:46.000000000 +0800
+++ a/kernel/timer.c	2010-05-25 06:17:44.000000000 +0800
@@ -748,14 +748,15 @@
  unsigned long apply_slack(struct timer_list *timer, unsigned long expires)
  {
  	unsigned long expires_limit, mask;
+	unsigned long now = jiffies;
  	int bit;

  	expires_limit = expires;

-	if (timer->slack > -1)
+	if (timer->slack >= 0)
  		expires_limit = expires + timer->slack;
-	else if (time_after(expires, jiffies)) /* auto slack: use 0.4% */
-		expires_limit = expires + (expires - jiffies)/256;
+	else if (time_after(expires, now)) /* auto slack: use 0.4% */
+		expires_limit = expires + (expires - now)/256;

  	mask = expires ^ expires_limit;
  	if (mask == 0)

--
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