netdev - Re: [PATCH repost for-3.9] pci: avoid work_on

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Message-ID: <20130411192005.GN17641@mtj.dyndns.org>
Date:	Thu, 11 Apr 2013 12:20:05 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Or Gerlitz <ogerlitz@...lanox.com>,
	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	David Miller <davem@...emloft.net>,
	Roland Dreier <roland@...nel.org>,
	netdev <netdev@...r.kernel.org>, Yan Burman <yanb@...lanox.com>,
	Jack Morgenstein <jackm@....mellanox.co.il>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH repost for-3.9] pci: avoid work_on_cpu for nested SRIOV
 probes

On Thu, Apr 11, 2013 at 10:17:17PM +0300, Michael S. Tsirkin wrote:
> Hmm no, there's a real deadlock here: you are
> trying to flush from work1 from within work2 running
> on same workqueue. work2 can't event start running.
> The problem is not annotation.

No, that has changed years ago with introduction of cmwq.  System
workqueues are now expected to have high enough maximum concurrency to
not cause deadlock as long as memory for worker creation is available,
so as long as your work item doesn't directly sit in the memory
reclaim path, it's safe to flush a different work item running on the
same workqueue with sufficiently high max_active.

Thanks.

-- 
tejun
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