linux-kernel - Re: [PATCH] sched: fix divide by zero at {thread_group,task}

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Date:	Wed, 08 Aug 2012 22:08:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <efault@....de>
Cc:	Stanislaw Gruszka <sgruszka@...hat.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] sched: fix divide by zero at {thread_group,task}_times

On Wed, 2012-08-08 at 21:50 +0200, Mike Galbraith wrote:
> 32bit built do_div()
> and div64_u64() both sucked equally compared to 64bit 

/me peeks at div64_u64 fallback implementation and sees why, it still
does a single div, it does some neat fls tricks.

Ok, no point in avoiding this then.. 

I did the below little edit, no point in mixing the old and new
primitives.. those __force things annoy me, but I guess otherwise we'll
upset sparse.

---
Index: linux-2.6/kernel/sched/core.c
===================================================================
--- linux-2.6.orig/kernel/sched/core.c
+++ linux-2.6/kernel/sched/core.c
@@ -3149,7 +3149,7 @@ static cputime_t scale_utime(cputime_t u
 	temp *= (__force u64) utime;
 
 	if (sizeof(cputime_t) == 4)
-		do_div(temp, (__force u32) total);
+		temp = div_u64(temp, (__force u32) total);
 	else
 		temp = div64_u64(temp, (__force u64) total);
 


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