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

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Message-ID: <20130411180517.GJ17641@mtj.dyndns.org>
Date:	Thu, 11 Apr 2013 11:05:17 -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

Hello,

On Thu, Apr 11, 2013 at 06:30:30PM +0300, Michael S. Tsirkin wrote:
> The issue is that a driver, in it's probe function, calls
> pci_sriov_enable so a PF device probe causes VF probe (AKA nested
> probe).  Each probe in pci_device_probe is (normally) run through
> work_on_cpu (this is to get the right numa node for memory allocated by
> the driver).  In turn work_on_cpu does this internally:
> 
>         schedule_work_on(cpu, &wfc.work);
>         flush_work(&wfc.work);
> 
> So if you are running probe on CPU1, and cause another
> probe on the same CPU, this will try to flush
> workqueue from inside same workqueue which of course
> deadlocks.
> 
> Nested probing might be tricky to get right generally.

Hmm... how about adding a work_on_cpu_nested() which takes @subclass
argument?  Wouldn't that be much cleaner?

Thanks.

-- 
tejun
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