netdev - Re: [Bugme-new] [Bug 8668] New: HTB Deadlock

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Date:	Mon, 25 Jun 2007 11:28:58 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	netdev@...r.kernel.org,
	"bugme-daemon@...nel-bugs.osdl.org" 
	<bugme-daemon@...nel-bugs.osdl.org>, ranko@...dernet.net
Subject: Re: [Bugme-new] [Bug 8668] New: HTB Deadlock

Andrew Morton wrote:
> On Sun, 24 Jun 2007 21:57:19 -0700 (PDT) bugme-daemon@...zilla.kernel.org wrote:
> 
>>I've been experiencing problems with HTB where the whole machine locks
>>up. This usually happens when the whole qdisc is being removed and
>>occasionally when a leaf is being removed.


It shouldn't happen when leaves are removed, you might be running
into some endless dequeue loops however that got fixed in 2.6.20.

>>Common is that it always happens when some sort of removal is in
>>progress.
>>
>>Console output I have captured is at the end of this message. The same
>>behavior exists from vanilla 2.6.19.7 and above. It is possible that the
>>problem also exist in the earlier versions however I did not go further
>>back.
>>
>>I also believe I have found where the actual problem is:
>>
>>qdisc_destroy() function is always called with dev->queue_lock locked.
>>htb_destroy() function up the stack is using del_timer_sync() call to
>>deactivate HTB qdisc timers. 
> 
> 
> yep, I would agree with that analysis.  del_timer_sync() under a lock is
> quite dangerous in this regard.
> 
> If the (misspelled) comment over htb_destroy() is true, current mainline
> appears still to have this bug.


It is. This patch I had originally planned for 2.6.23 switches HTB
to the generic estimator, which shouldn't suffer from this.

Ranko, can you try if it fixes your timer problem?
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