From: Ming Lei <ming.lei@canonical.com>
To: Wedson Almeida Filho <wedsonaf@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>,
Greg KH <gregkh@linuxfoundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
Linux PM List <linux-pm@vger.kernel.org>
Subject: Re: Race condition between driver_probe_device and device_shutdown
Date: Fri, 7 Dec 2012 21:04:19 +0800 [thread overview]
Message-ID: <CACVXFVMOxQEJ-nrvGQ-PkevqKkLnXu+QjHgeswkbzFjqOVYCdQ@mail.gmail.com> (raw)
In-Reply-To: <CANeycqqO06+u6Qy3zL=G_a=_sTYDOzUYf8wu7B7RGFJfuGNoRg@mail.gmail.com>
On Fri, Dec 7, 2012 at 8:16 PM, Wedson Almeida Filho <wedsonaf@gmail.com> wrote:
>> Because device_del() will put reference count of the parent, and the patch
>> only focuses on race between probe/release and shutdown.
>
> Right. device_del() puts the reference count of the parent -- is it
> guaranteed that device_del() won't ever reassign dev->parent though
> (e.g., to NULL)? I don't think it is, so I think that patch should
> also save the pointer to the parent and use it (instead of what
> happens to be in than dev->parent) to release the lock and put the
> ref.
>
>> As far as device_move() concerned, looks it might be a problem.
>> The problem even exits on driver attach vs. device open/release,
>> if device_move is called in open() and open() happens before driver
>> attach completes.
>
> Yeah, the pattern of locking the parent followed by the device occurs
> in a few places. It looks like they were added by Alan with commit
> bf74ad5bc41727d5f2f1c6bedb2c1fac394de731. (And as Greg mentioned,
> might be occurring often enough to merit being moved into a common
> function.)
In fact, there is no shutdown callback defined for usb driver, so holding
the parent lock in device_shutdown() might be removed.
>
> I guess the question is whether the callee is allowed to call
> device_move(), if not, we're good.
Not only the callee, and other contexts can change device->parent
too. Looks rfcomm_tty_open() which calls device_move() is called
in open() context, so the parent might be changed before unlock(dev->parent)
in __driver_attach().
>
>> Your concern on device_remove() might be correct. Also, I am wondering
>> if we can walk the 'dpm_list' backwards for device shutdown, which should
>> be simpler and more reasonable.
>
> How would that help?
device_pm_lock() can prevent device_move() from being running.
Thanks,
--
Ming Lei
next prev parent reply other threads:[~2012-12-07 13:04 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-18 4:59 Race condition between driver_probe_device and device_shutdown Greg KH
2012-05-20 14:08 ` Ming Lei
2012-05-20 19:51 ` Greg KH
2012-05-21 4:53 ` Ming Lei
2012-05-21 18:29 ` Alan Stern
2012-05-22 0:35 ` Ming Lei
2012-05-22 14:11 ` Alan Stern
2012-05-22 19:16 ` Eric W. Biederman
2012-05-23 10:05 ` Ming Lei
2012-05-23 15:06 ` Alan Stern
2012-05-24 1:39 ` Ming Lei
2012-05-24 2:14 ` Greg KH
2012-05-24 3:12 ` Ming Lei
2012-05-24 14:37 ` Alan Stern
2012-05-25 0:33 ` Ming Lei
2012-12-06 9:11 ` Race condition between driver_probe_device and device_shutdown Wedson Almeida Filho
2012-12-06 10:52 ` Ming Lei
2012-12-07 0:09 ` Wedson Almeida Filho
2012-12-07 3:42 ` Ming Lei
2012-12-07 12:16 ` Wedson Almeida Filho
2012-12-07 13:04 ` Ming Lei [this message]
2012-12-07 15:25 ` Alan Stern
2012-12-07 16:27 ` Ming Lei
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