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Date: Sat, 30 Nov 2013 01:31:33 +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 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.
Thanks,
Rafael
---
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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