linux-kernel - Re: [PATCH v2 04/10] PCI: Destroy pci dev only once

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Message-ID: <CAE9FiQXevSPmPEvxzXjC-CFhpYHic0v+vN5+JV3j5kmX-wv_GQ@mail.gmail.com>
Date:	Tue, 26 Nov 2013 18:26:54 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Gu Zheng <guz.fnst@...fujitsu.com>,
	Guo Chao <yan@...ux.vnet.ibm.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/10] PCI: Destroy pci dev only once

On Tue, Nov 26, 2013 at 5:24 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> So assume pci_destroy_dev() is called twice in parallel for the same dev
> by two different threads.  Thread 1 does the atomic_inc_and_test() and
> finds that it is OK to do the device_del() and put_device() which causes
> the device object to be freed.  Then thread 2 does the atomic_inc_and_test()
> on the already freed device object and crashes the kernel.
>
thread2 should still hold one extra reference.
that is in
  device_schedule_callback
     ==> sysfs_schedule_callback
         ==> kobject_get(kobj)

pci_destroy_dev for thread2 is called at this point.

and that reference will be released from
        sysfs_schedule_callback
        ==> kobject_put()...

Thanks

Yinghai
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