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

[Jeff Chua <jeff.chua.linux@gmail.com>]

On Mon, May 24, 2010 at 10:57 PM, Linus Torvalds <torvalds@linux-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)