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Message-ID: <3407940.L2vvqCPqy4@vostro.rjw.lan>
Date: Mon, 13 Jan 2014 02:03:16 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Yinghai Lu <yinghai@...nel.org>
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>,
Mika Westerberg <mika.westerberg@...ux.intel.com>,
Myron Stowe <myron.stowe@...il.com>
Subject: [PATCH] PCI / remove: Check parent kobject in pci_destroy_dev() (was: Re: [PATCH v2 04/10] PCI: Destroy pci dev only once)
On Saturday, December 07, 2013 02:27:51 AM Rafael J. Wysocki wrote:
> On Thursday, December 05, 2013 10:52:36 PM Yinghai Lu wrote:
> > On Mon, Dec 2, 2013 at 6:49 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > >
> > > Scenario 5: pci_stop_and_remove_bus_device() is run concurrently
> > > for a device and its parent bridge via remove_callback().
> > >
> > > In that case both code paths attempt to acquire
> > > pci_remove_rescan_mutex. If the child device removal acquires
> > > it first, there will be no problems. However, if the parent
> > > bridge removal acquires it first, it will eventually execute
> > > pci_destroy_dev() for the child device, but that device will
> > > not be freed yet due to the reference held by the concurrent
> > > child removal. Consequently, both pci_stop_bus_device() and
> > > pci_remove_bus_device() will be executed for that device
> > > unnecessarily and pci_destroy_dev() will see a corrupted list
> > > head in that object. Moreover, an excess put_device() will
> > > be executed for that device in that case which may lead to a
> > > use-after-free in the final kobject_put() done by
> > > sysfs_schedule_callback_work().
> > >
> > > Index: linux-pm/include/linux/pci.h
> > > ===================================================================
> > > --- linux-pm.orig/include/linux/pci.h
> > > +++ linux-pm/include/linux/pci.h
> > > @@ -321,6 +321,7 @@ struct pci_dev {
> > > unsigned int multifunction:1;/* Part of multi-function device */
> > > /* keep track of device state */
> > > unsigned int is_added:1;
> > > + unsigned int is_gone:1;
> > > unsigned int is_busmaster:1; /* device is busmaster */
> > > unsigned int no_msi:1; /* device may not use msi */
> > > unsigned int block_cfg_access:1; /* config space access is blocked */
> > > Index: linux-pm/drivers/pci/remove.c
> > > ===================================================================
> > > --- linux-pm.orig/drivers/pci/remove.c
> > > +++ linux-pm/drivers/pci/remove.c
> > > @@ -34,6 +34,7 @@ static void pci_stop_dev(struct pci_dev
> > >
> > > static void pci_destroy_dev(struct pci_dev *dev)
> > > {
> > > + dev->is_gone = 1;
> > > device_del(&dev->dev);
> > >
> > > down_write(&pci_bus_sem);
> > > @@ -109,8 +110,10 @@ static void pci_remove_bus_device(struct
> > > */
> > > void pci_stop_and_remove_bus_device(struct pci_dev *dev)
> > > {
> > > - pci_stop_bus_device(dev);
> > > - pci_remove_bus_device(dev);
> > > + if (!dev->is_gone) {
> > > + pci_stop_bus_device(dev);
> > > + pci_remove_bus_device(dev);
> > > + }
> > > }
> > > EXPORT_SYMBOL(pci_stop_and_remove_bus_device);
> > >
> >
> > Yes, above change should address sys double remove problem.
>
> I've just realized that we don't need a new flag for that, though.
>
> It looks like we only need to check dev->dev.kobj.parent and return if that is
> NULL, because that means pci_destroy_dev() has run for that device already
> (I'm wondering why device_del() doesn't clear dev->parent, BTW, it looks like
> it should do that?).
>
> Of course, that still is going to be racy if we don't hold
> pci_remove_rescan_mutex around pci_stop_and_remove_bus_device() in every code
> path using it (or use another similar synchronization mechanism).
Before I forget about this, on top of the series I sent out on Friday.
Thanks,
Rafael
---
From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Subject: PCI / remove: Check parent kobject in pci_destroy_dev()
If pci_stop_and_remove_bus_device() is run concurrently for a device
and its parent bridge via remove_callback(), both code paths attempt
to acquire pci_rescan_remove_lock. If the child device removal
acquires it first, there will be no problems. However, if the parent
bridge removal acquires it first, it will eventually execute
pci_destroy_dev() for the child device, but that device object will
not be freed yet due to the reference held by the concurrent child
removal. Consequently, both pci_stop_bus_device() and
pci_remove_bus_device() will be executed for that device unnecessarily
and pci_destroy_dev() will see a corrupted list head in that object.
Moreover, an excess put_device() will be executed for that device in
that case which may lead to a use-after-free in the final
kobject_put() done by sysfs_schedule_callback_work().
To avoid that problem, make pci_destroy_dev() check if the device's
parent kobject is NULL, which only happens after device_del() has
already run for it. Make pci_destroy_dev() return immediately
whithout doing anything in that case.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
drivers/pci/remove.c | 3 +++
1 file changed, 3 insertions(+)
Index: linux-pm/drivers/pci/remove.c
===================================================================
--- linux-pm.orig/drivers/pci/remove.c
+++ linux-pm/drivers/pci/remove.c
@@ -34,6 +34,9 @@ static void pci_stop_dev(struct pci_dev
static void pci_destroy_dev(struct pci_dev *dev)
{
+ if (!dev->dev.kobj.parent)
+ return;
+
device_del(&dev->dev);
down_write(&pci_bus_sem);
--
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