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SubjectRe: pci_walk_bus race condition
From
Date
On Mon, 2006-05-29 at 16:05, Zhang, Yanmin wrote:
> On Mon, 2006-05-29 at 08:41, Zhang, Yanmin wrote:
> > On Fri, 2006-05-26 at 21:50, Greg KH wrote:
> > > On Fri, May 26, 2006 at 02:35:16PM +0800, Zhang, Yanmin wrote:
> > > > pci_walk_bus has a race with pci_destroy_dev. In the while loop,
> > > > when the callback function is called, dev pointed by next might be
> > > > freed and erased. So later on access to dev might cause kernel panic.
> > >
> > > Have you seen this happen? The only user of this function is the PPC64
> > > EEH handler, which last time I checked, didn't run on Intel based
> > > processors :)
> > I am enabling PCI-Express AER in kernel and want to use it. After
> > double-checking, I found the lock is not good.
> How about changing pci_bus_lock to a sema? I think it's the thorough
> approach. As the write lock is used only when initializing and uninitializing,
> the performance won't be hurted severely.
Here is the patch.

From: Zhang Yanmin <yanmin.zhang@intel.com>

pci_walk_bus has a race with pci_destroy_dev. When cb is called
in pci_walk_bus, pci_destroy_dev might unlink the dev pointed by next.
Later on in the next loop, pointer next becomes NULL and cause
kernel panic.

Below patch against 2.6.17-rc4 fixes it by changing pci_bus_lock (spin_lock)
to pci_bus_sem (rw_semaphore).

Signed-off-by: Zhang Yanmin <yanmin.zhang@intel.com>

---

diff -Nraup linux-2.6.17-rc4/drivers/pci/bus.c linux-2.6.17-rc4_pci_bus_lock/drivers/pci/bus.c
--- linux-2.6.17-rc4/drivers/pci/bus.c 2006-04-20 21:19:24.000000000 +0800
+++ linux-2.6.17-rc4_pci_bus_lock/drivers/pci/bus.c 2006-06-01 09:24:56.000000000 +0800
@@ -81,9 +81,9 @@ void __devinit pci_bus_add_device(struct
{
device_add(&dev->dev);

- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_add_tail(&dev->global_list, &pci_devices);
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);

pci_proc_attach_device(dev);
pci_create_sysfs_dev_files(dev);
@@ -125,10 +125,10 @@ void __devinit pci_bus_add_devices(struc
*/
if (dev->subordinate) {
if (list_empty(&dev->subordinate->node)) {
- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_add_tail(&dev->subordinate->node,
&dev->bus->children);
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);
}
pci_bus_add_devices(dev->subordinate);

@@ -168,7 +168,7 @@ void pci_walk_bus(struct pci_bus *top, v
struct list_head *next;

bus = top;
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);
next = top->devices.next;
for (;;) {
if (next == &bus->devices) {
@@ -180,22 +180,19 @@ void pci_walk_bus(struct pci_bus *top, v
continue;
}
dev = list_entry(next, struct pci_dev, bus_list);
- pci_dev_get(dev);
if (dev->subordinate) {
/* this is a pci-pci bridge, do its devices next */
next = dev->subordinate->devices.next;
bus = dev->subordinate;
} else
next = dev->bus_list.next;
- spin_unlock(&pci_bus_lock);

- /* Run device routines with the bus unlocked */
+ /* Run device routines with the device locked */
+ down(&dev->dev.sem);
cb(dev, userdata);
-
- spin_lock(&pci_bus_lock);
- pci_dev_put(dev);
+ up(&dev->dev.sem);
}
- spin_unlock(&pci_bus_lock);
+ up_read(&pci_bus_sem);
}
EXPORT_SYMBOL_GPL(pci_walk_bus);

diff -Nraup linux-2.6.17-rc4/drivers/pci/pci.h linux-2.6.17-rc4_pci_bus_lock/drivers/pci/pci.h
--- linux-2.6.17-rc4/drivers/pci/pci.h 2006-05-17 17:16:24.000000000 +0800
+++ linux-2.6.17-rc4_pci_bus_lock/drivers/pci/pci.h 2006-05-31 15:07:48.000000000 +0800
@@ -40,7 +40,7 @@ extern int pci_bus_find_capability (stru
extern void pci_remove_legacy_files(struct pci_bus *bus);

/* Lock for read/write access to pci device and bus lists */
-extern spinlock_t pci_bus_lock;
+extern struct rw_semaphore pci_bus_sem;

#ifdef CONFIG_X86_IO_APIC
extern int pci_msi_quirk;
diff -Nraup linux-2.6.17-rc4/drivers/pci/probe.c linux-2.6.17-rc4_pci_bus_lock/drivers/pci/probe.c
--- linux-2.6.17-rc4/drivers/pci/probe.c 2006-05-17 17:16:24.000000000 +0800
+++ linux-2.6.17-rc4_pci_bus_lock/drivers/pci/probe.c 2006-05-31 15:13:38.000000000 +0800
@@ -377,9 +377,9 @@ struct pci_bus * __devinit pci_add_new_b

child = pci_alloc_child_bus(parent, dev, busnr);
if (child) {
- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_add_tail(&child->node, &parent->children);
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);
}
return child;
}
@@ -838,9 +838,9 @@ void __devinit pci_device_add(struct pci
* and the bus list for fixup functions, etc.
*/
INIT_LIST_HEAD(&dev->global_list);
- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_add_tail(&dev->bus_list, &bus->devices);
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);
}

struct pci_dev * __devinit
@@ -975,9 +975,10 @@ struct pci_bus * __devinit pci_create_bu
pr_debug("PCI: Bus %04x:%02x already known\n", pci_domain_nr(b), bus);
goto err_out;
}
- spin_lock(&pci_bus_lock);
+
+ down_write(&pci_bus_sem);
list_add_tail(&b->node, &pci_root_buses);
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);

memset(dev, 0, sizeof(*dev));
dev->parent = parent;
@@ -1017,9 +1018,9 @@ class_dev_create_file_err:
class_dev_reg_err:
device_unregister(dev);
dev_reg_err:
- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_del(&b->node);
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);
err_out:
kfree(dev);
kfree(b);
diff -Nraup linux-2.6.17-rc4/drivers/pci/remove.c linux-2.6.17-rc4_pci_bus_lock/drivers/pci/remove.c
--- linux-2.6.17-rc4/drivers/pci/remove.c 2006-04-20 21:19:24.000000000 +0800
+++ linux-2.6.17-rc4_pci_bus_lock/drivers/pci/remove.c 2006-05-31 15:15:26.000000000 +0800
@@ -22,18 +22,18 @@ static void pci_destroy_dev(struct pci_d
pci_proc_detach_device(dev);
pci_remove_sysfs_dev_files(dev);
device_unregister(&dev->dev);
- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_del(&dev->global_list);
dev->global_list.next = dev->global_list.prev = NULL;
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);
}

/* Remove the device from the device lists, and prevent any further
* list accesses from this device */
- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_del(&dev->bus_list);
dev->bus_list.next = dev->bus_list.prev = NULL;
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);

pci_free_resources(dev);
pci_dev_put(dev);
@@ -62,9 +62,9 @@ void pci_remove_bus(struct pci_bus *pci_
{
pci_proc_detach_bus(pci_bus);

- spin_lock(&pci_bus_lock);
+ down_write(&pci_bus_sem);
list_del(&pci_bus->node);
- spin_unlock(&pci_bus_lock);
+ up_write(&pci_bus_sem);
pci_remove_legacy_files(pci_bus);
class_device_remove_file(&pci_bus->class_dev,
&class_device_attr_cpuaffinity);
diff -Nraup linux-2.6.17-rc4/drivers/pci/search.c linux-2.6.17-rc4_pci_bus_lock/drivers/pci/search.c
--- linux-2.6.17-rc4/drivers/pci/search.c 2006-05-17 17:16:24.000000000 +0800
+++ linux-2.6.17-rc4_pci_bus_lock/drivers/pci/search.c 2006-05-31 11:03:45.000000000 +0800
@@ -13,7 +13,7 @@
#include <linux/interrupt.h>
#include "pci.h"

-DEFINE_SPINLOCK(pci_bus_lock);
+DECLARE_RWSEM(pci_bus_sem);

static struct pci_bus * __devinit
pci_do_find_bus(struct pci_bus* bus, unsigned char busnr)
@@ -72,11 +72,11 @@ pci_find_next_bus(const struct pci_bus *
struct pci_bus *b = NULL;

WARN_ON(in_interrupt());
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);
n = from ? from->node.next : pci_root_buses.next;
if (n != &pci_root_buses)
b = pci_bus_b(n);
- spin_unlock(&pci_bus_lock);
+ up_read(&pci_bus_sem);
return b;
}

@@ -124,7 +124,7 @@ struct pci_dev * pci_get_slot(struct pci
struct pci_dev *dev;

WARN_ON(in_interrupt());
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);

list_for_each(tmp, &bus->devices) {
dev = pci_dev_b(tmp);
@@ -135,7 +135,7 @@ struct pci_dev * pci_get_slot(struct pci
dev = NULL;
out:
pci_dev_get(dev);
- spin_unlock(&pci_bus_lock);
+ up_read(&pci_bus_sem);
return dev;
}

@@ -167,7 +167,7 @@ static struct pci_dev * pci_find_subsys(
struct pci_dev *dev;

WARN_ON(in_interrupt());
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);
n = from ? from->global_list.next : pci_devices.next;

while (n && (n != &pci_devices)) {
@@ -181,7 +181,7 @@ static struct pci_dev * pci_find_subsys(
}
dev = NULL;
exit:
- spin_unlock(&pci_bus_lock);
+ up_read(&pci_bus_sem);
return dev;
}

@@ -232,7 +232,7 @@ pci_get_subsys(unsigned int vendor, unsi
struct pci_dev *dev;

WARN_ON(in_interrupt());
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);
n = from ? from->global_list.next : pci_devices.next;

while (n && (n != &pci_devices)) {
@@ -247,7 +247,7 @@ pci_get_subsys(unsigned int vendor, unsi
dev = NULL;
exit:
dev = pci_dev_get(dev);
- spin_unlock(&pci_bus_lock);
+ up_read(&pci_bus_sem);
pci_dev_put(from);
return dev;
}
@@ -292,7 +292,7 @@ pci_find_device_reverse(unsigned int ven
struct pci_dev *dev;

WARN_ON(in_interrupt());
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);
n = from ? from->global_list.prev : pci_devices.prev;

while (n && (n != &pci_devices)) {
@@ -304,7 +304,7 @@ pci_find_device_reverse(unsigned int ven
}
dev = NULL;
exit:
- spin_unlock(&pci_bus_lock);
+ up_read(&pci_bus_sem);
return dev;
}

@@ -328,7 +328,7 @@ struct pci_dev *pci_get_class(unsigned i
struct pci_dev *dev;

WARN_ON(in_interrupt());
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);
n = from ? from->global_list.next : pci_devices.next;

while (n && (n != &pci_devices)) {
@@ -340,7 +340,7 @@ struct pci_dev *pci_get_class(unsigned i
dev = NULL;
exit:
dev = pci_dev_get(dev);
- spin_unlock(&pci_bus_lock);
+ up_read(&pci_bus_sem);
pci_dev_put(from);
return dev;
}
@@ -362,7 +362,7 @@ int pci_dev_present(const struct pci_dev
int found = 0;

WARN_ON(in_interrupt());
- spin_lock(&pci_bus_lock);
+ down_read(&pci_bus_sem);
while (ids->vendor || ids->subvendor || ids->class_mask) {
list_for_each_entry(dev, &pci_devices, global_list) {
if (pci_match_one_device(ids, dev)) {
@@ -372,8 +372,8 @@ int pci_dev_present(const struct pci_dev
}
ids++;
}
-exit:
- spin_unlock(&pci_bus_lock);
+exit:
+ up_read(&pci_bus_sem);
return found;
}
EXPORT_SYMBOL(pci_dev_present);
-
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