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Date: Sat, 30 Nov 2013 22:37:21 +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>
Subject: Re: [PATCH v2 04/10] PCI: Destroy pci dev only once
On Saturday, November 30, 2013 01:31:33 AM Rafael J. Wysocki wrote:
> On Saturday, November 30, 2013 12:45:55 AM Rafael J. Wysocki wrote:
> > On Saturday, November 30, 2013 12:38:26 AM Rafael J. Wysocki wrote:
> > > On Tuesday, November 26, 2013 06:26:54 PM Yinghai Lu wrote:
> > > > 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()...
> > >
> > > Well, that would be the case if thread 2 was started by device_schedule_callback(),
> > > but again, for example, it may be trim_stale_devices() started by acpiphp_check_bridge()
> > > that doesn't hold extra references to the pci_dev. [Well, that piece of code
> > > is racy anyway, because it walks bus->devices without locking. Which is my
> > > fault too, because I overlooked that. Shame, shame.]
> > >
> > > Perhaps we can do something like the (untested) patch below (in addition to the
> > > $subject patch). Do you see any immediate problems with it?
> >
> > Ah, I see one. It will break pci_stop_bus_device() and pci_remove_bus_device().
> > So much for being clever.
> >
> > Moreover, it looks like those two routines above are racy too for the same
> > reason?
>
> The (still untested) patch below is what I have come up with for now. The
> is_gone flag is now only operated under pci_remove_rescan_mutex, so it need
> not be atomic. Of course, whoever calls pci_stop_and_remove_bus_device()
> (the "locked" one) should hold a ref to the device being removed to avoid
> use-after-free (the callers need to be audited for that).
>
> Well, I probably still missed something, because it's the middle of the night
> and I should be going to sleep instead of starig at the PCI removal code. Sigh.
Thunderbolt hotplug works for me with this patch applied FWIW.
> ---
> drivers/pci/hotplug/acpiphp_glue.c | 15 ++++++++++++---
> drivers/pci/pci-sysfs.c | 17 ++++++++++++-----
> drivers/pci/pci.h | 3 +++
> drivers/pci/remove.c | 15 +++++++++++++--
> include/linux/pci.h | 1 +
> 5 files changed, 41 insertions(+), 10 deletions(-)
>
> Index: linux-pm/drivers/pci/hotplug/acpiphp_glue.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/hotplug/acpiphp_glue.c
> +++ linux-pm/drivers/pci/hotplug/acpiphp_glue.c
> @@ -553,6 +553,8 @@ static void __ref enable_slot(struct acp
> int max, pass;
> LIST_HEAD(add_list);
>
> + lock_pci_remove_rescan();
> +
> acpiphp_rescan_slot(slot);
> max = acpiphp_max_busnr(bus);
> for (pass = 0; pass < 2; pass++) {
> @@ -586,6 +588,8 @@ static void __ref enable_slot(struct acp
>
> pci_bus_add_devices(bus);
>
> + unlock_pci_remove_rescan();
> +
> slot->flags |= SLOT_ENABLED;
> list_for_each_entry(func, &slot->funcs, sibling) {
> dev = pci_get_slot(bus, PCI_DEVFN(slot->device,
> @@ -626,6 +630,7 @@ static void disable_slot(struct acpiphp_
> struct acpiphp_func *func;
> struct pci_dev *pdev;
>
> + lock_pci_remove_rescan();
> /*
> * enable_slot() enumerates all functions in this device via
> * pci_scan_slot(), whether they have associated ACPI hotplug
> @@ -633,9 +638,10 @@ static void disable_slot(struct acpiphp_
> * here.
> */
> while ((pdev = dev_in_slot(slot))) {
> - pci_stop_and_remove_bus_device(pdev);
> + __pci_stop_and_remove_bus_device(pdev);
> pci_dev_put(pdev);
> }
> + unlock_pci_remove_rescan();
>
> list_for_each_entry(func, &slot->funcs, sibling)
> acpiphp_bus_trim(func_to_handle(func));
> @@ -710,7 +716,7 @@ static void trim_stale_devices(struct pc
> alive = pci_bus_read_dev_vendor_id(dev->bus, dev->devfn, &v, 0);
> }
> if (!alive) {
> - pci_stop_and_remove_bus_device(dev);
> + __pci_stop_and_remove_bus_device(dev);
> if (handle)
> acpiphp_bus_trim(handle);
> } else if (bus) {
> @@ -743,12 +749,15 @@ static void acpiphp_check_bridge(struct
> mutex_lock(&slot->crit_sect);
> /* wake up all functions */
> if (get_slot_status(slot) == ACPI_STA_ALL) {
> + lock_pci_remove_rescan();
> +
> /* remove stale devices if any */
> list_for_each_entry_safe(dev, tmp, &bus->devices,
> bus_list)
> if (PCI_SLOT(dev->devfn) == slot->device)
> trim_stale_devices(dev);
>
> + unlock_pci_remove_rescan();
> /* configure all functions */
> enable_slot(slot);
> } else {
> @@ -783,7 +792,7 @@ static void acpiphp_sanitize_bus(struct
> res->end) {
> /* Could not assign a required resources
> * for this device, remove it */
> - pci_stop_and_remove_bus_device(dev);
> + __pci_stop_and_remove_bus_device(dev);
> break;
> }
> }
> Index: linux-pm/drivers/pci/pci-sysfs.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-sysfs.c
> +++ linux-pm/drivers/pci/pci-sysfs.c
> @@ -298,6 +298,17 @@ msi_bus_store(struct device *dev, struct
> static DEVICE_ATTR_RW(msi_bus);
>
> static DEFINE_MUTEX(pci_remove_rescan_mutex);
> +
> +void lock_pci_remove_rescan(void)
> +{
> + mutex_lock(&pci_remove_rescan_mutex);
> +}
> +
> +void unlock_pci_remove_rescan(void)
> +{
> + mutex_unlock(&pci_remove_rescan_mutex);
> +}
> +
> static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf,
> size_t count)
> {
> @@ -354,11 +365,7 @@ static struct device_attribute dev_resca
>
> static void remove_callback(struct device *dev)
> {
> - struct pci_dev *pdev = to_pci_dev(dev);
> -
> - mutex_lock(&pci_remove_rescan_mutex);
> - pci_stop_and_remove_bus_device(pdev);
> - mutex_unlock(&pci_remove_rescan_mutex);
> + pci_stop_and_remove_bus_device(to_pci_dev(dev));
> }
>
> static ssize_t
> Index: linux-pm/drivers/pci/pci.h
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci.h
> +++ linux-pm/drivers/pci/pci.h
> @@ -11,8 +11,11 @@ extern const unsigned char pcie_link_spe
>
> /* Functions internal to the PCI core code */
>
> +void lock_pci_remove_rescan(void);
> +void unlock_pci_remove_rescan(void);
> int pci_create_sysfs_dev_files(struct pci_dev *pdev);
> void pci_remove_sysfs_dev_files(struct pci_dev *pdev);
> +void __pci_stop_and_remove_bus_device(struct pci_dev *pdev);
> #if !defined(CONFIG_DMI) && !defined(CONFIG_ACPI)
> static inline void pci_create_firmware_label_files(struct pci_dev *pdev)
> { return; }
> Index: linux-pm/drivers/pci/remove.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/remove.c
> +++ linux-pm/drivers/pci/remove.c
> @@ -34,6 +34,10 @@ static void pci_stop_dev(struct pci_dev
>
> static void pci_destroy_dev(struct pci_dev *dev)
> {
> + if (dev->is_gone)
> + return;
> +
> + dev->is_gone = 1;
> device_del(&dev->dev);
>
> down_write(&pci_bus_sem);
> @@ -95,6 +99,12 @@ static void pci_remove_bus_device(struct
> pci_destroy_dev(dev);
> }
>
> +void __pci_stop_and_remove_bus_device(struct pci_dev *dev)
> +{
> + pci_stop_bus_device(dev);
> + pci_remove_bus_device(dev);
> +}
> +
> /**
> * pci_stop_and_remove_bus_device - remove a PCI device and any children
> * @dev: the device to remove
> @@ -109,8 +119,9 @@ 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);
> + lock_pci_remove_rescan();
> + __pci_stop_and_remove_bus_device(dev);
> + unlock_pci_remove_rescan();
> }
> EXPORT_SYMBOL(pci_stop_and_remove_bus_device);
>
> 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 */
>
> --
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--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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