netdev - Re: [PATCH 1/2] tcp-lp 2.6.18-rc6: fix tcp_lp_remote_hz

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Date:	Sun, 10 Dec 2006 22:40:55 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	frankvm@...nkvm.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] tcp-lp 2.6.18-rc6: fix
 tcp_lp_remote_hz_estimator() about rhz

From: Frank van Maarseveen <frankvm@...nkvm.com>
Date: Sun, 3 Dec 2006 13:32:07 +0100

> On Mon, Sep 04, 2006 at 05:44:58PM +0800, Wong Edison wrote:
> > pageexec report an oops for tcp_lp_owd_calculator(). This is due to
> > tcp_lp_remote_hz_estimator can return 0.
> > 
> > This patch fix the handling of lp->flag, so will set lp->flag as FALSE
> > if rhz <= 0
> > 
> > Signed-off-by: Wong Hoi Sing Edison <hswong3i@...il.com>
> > 
> > ---
> > 
> > diff -urpN 2.6.18-rc6/tcp_lp.c tcp-lp/tcp_lp.c
> > --- 2.6.18-rc6/tcp_lp.c	2006-09-04 16:21:00.000000000 +0800
> > +++ tcp-lp/tcp_lp.c	2006-09-04 17:22:19.000000000 +0800
> > @@ -153,14 +157,17 @@ static u32 tcp_lp_remote_hz_estimator(st
> > 	if (m < 0)
> > 		m = -m;
> > 
> > -	if (rhz != 0) {
> > +	if (rhz > 0) {
> > 		m -= rhz >> 6;	/* m is now error in remote HZ est */
> > 		rhz += m;	/* 63/64 old + 1/64 new */
> > 	} else
> > 		rhz = m << 6;
> > 
> > 	/* record time for successful remote HZ calc */
> > -	lp->flag |= LP_VALID_RHZ;
> > +	if (rhz > 0)
> > +		lp->flag |= LP_VALID_RHZ;
> > +	else
> > +		lp->flag &= ~LP_VALID_RHZ;
> > 
> >  out:
> > 	/* record reference time stamp */
> > 
> > -- 
> > VGER BF report: U 0.500057
> 
> Got bitten by this zerodivide in 2.6.18.* (every few days a panic inside
> an interrupt handler) and it doesn't seem to be fixed in 2.6.19.

That patch doesn't even apply, because the following other
patch from Wong is in the tree which conflicts.  So I can't
apply this other fix of his, even if I wanted to.

commit bfbea8a8869a0e21b97605841d04190d63665d19
Author: Wong Hoi Sing Edison <hswong3i@...il.com>
Date:   Thu Sep 28 14:40:21 2006 -0700

    [TCP] tcp-lp: prevent chance for oops
    
    This patch fix the chance for tcp_lp_remote_hz_estimator return 0, if
    0 < rhz < 64. It also make sure the flag LP_VALID_RHZ is set
    correctly.
    
    Signed-off-by: Wong Hoi Sing Edison <hswong3i@...il.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

diff --git a/net/ipv4/tcp_lp.c b/net/ipv4/tcp_lp.c
index 308fb7e..f0ebaf0 100644
--- a/net/ipv4/tcp_lp.c
+++ b/net/ipv4/tcp_lp.c
@@ -31,8 +31,6 @@
  *   Hung Hing Lun, Mike <hlhung3i@...il.com>
  * SourceForge project page:
  *   http://tcp-lp-mod.sourceforge.net/
- *
- * Version: $Id: tcp_lp.c,v 1.24 2006/09/05 20:22:53 hswong3i Exp $
  */
 
 #include <linux/module.h>
@@ -164,7 +162,7 @@ static u32 tcp_lp_remote_hz_estimator(st
 
  out:
 	/* record time for successful remote HZ calc */
-	if (rhz > 0)
+	if ((rhz >> 6) > 0)
 		lp->flag |= LP_VALID_RHZ;
 	else
 		lp->flag &= ~LP_VALID_RHZ;
-
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