netdev - Re: [NET]: gen_estimator: fix locking and timer related bugs [Re: [Bugme-new] [Bug 8668] New: HTB Deadlock]

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Date:	Thu, 28 Jun 2007 11:13:40 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org,
	"bugme-daemon\@kernel-bugs\.osdl\.org" 
	<bugme-daemon@...nel-bugs.osdl.org>, ranko@...dernet.net
Subject: Re: [NET]: gen_estimator: fix locking and timer related bugs [Re: [Bugme-new] [Bug 8668] New: HTB Deadlock]

On Wed, Jun 27, 2007 at 05:25:45PM +0200, Patrick McHardy wrote:
...
> Additionally there are a few more related problems that seem to be
> relicts from the timer when the estimator was qdisc specific and
> could rely on the rtnl or dev->qdisc_lock:
> 
> - the check whether the list is empty and a timer needs to be started
>   when adding a new estimator doesn't take the lock, so it races
>   against concurrent additions, which can result in the timer beeing
>   added twice or getting reinitialized after being added.
> 
> - the new estimator's next pointer is also set without holding the
>   lock, again racing against concurrent additions with possible
>   list corruption as a result.
> 
> - the timer deletion when killing an estimator is also not under
>   the lock and races against timer arming when adding a new estimator.
> 
> Fix by holding the lock around the entire list addition and initial
> timer arming. Removal is not done explicitly anymore, instead the
> timer function only rearms the timer when there are still estimators
> present.
...
> @@ -202,7 +201,6 @@ void gen_kill_estimator(struct gnet_stats_basic *bstats,
>  	struct gen_estimator *est, **pest;
>  
>  	for (idx=0; idx <= EST_MAX_INTERVAL; idx++) {
> -		int killed = 0;
>  		pest = &elist[idx].list;
>  		while ((est=*pest) != NULL) {

So, maybe this list walking here needs some locking too?

Jarek P.
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