Subject: Re: [Bugme-new] [Bug 8736] New: New TC deadlock scenario

From: Patrick McHardy <[email-masked]>
Date: Wed, 11 Jul 2007 20:31:12 +0200

Andrew Morton wrote:
>>http://bugzilla.kernel.org/show_bug.cgi?id=8736
>>
>>Here is another scenario I bumped onto - qdisc_watchdog_cancel() and
>>qdisc_restart() deadlock.
>>
>>CPU#0
>>qdisc_watchdog() fires and gets dev->queue_lock
>>qdisc_run()...qdisc_restart()... 
>>-> releases dev->queue_lock and enters dev_hard_start_xmit()
>>
>>CPU#1
>>tc del qdisc dev ...
>>qdisc_graft()...dev_graft_qdisc()...dev_deactivate()...
>>-> grabs dev->queue_lock ... 
>>qdisc_reset()...{cbq,hfsc,htb,netem,tbf}_reset()...qdisc_watchdog_cancel()...
>>-> hrtimer_cancel() - waiting for the qdisc_watchdog() to exit, while still
>>holding dev->queue_lock
>>
>>CPU#0
>>dev_hard_start_xmit() returns ... 
>>-> wants to get dev->queue_lock(!)
>>
>>DEADLOCK!

Good catch.

Please try reverting commit 1936502d00ae6c2aa3931c42f6cf54afaba094f2,
that should fix it.