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SubjectRe: [BUG][PATCH] Fix race condition about network device name allocation
On Fri, 11 May 2007 14:40:45 +0900
Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com> wrote:

> Hi,
>
> I encountered the following error when I was hot-plugging network card
> using pci hotplug driver.
>
> kobject_add failed for eth8 with -EEXIST, don't try to register things with the same name in the same directory.
>
> Call Trace:
> [<a000000100013940>] show_stack+0x40/0xa0
> sp=e0000000652cfbf0 bsp=e0000000652c9450
> [<a0000001000139d0>] dump_stack+0x30/0x60
> sp=e0000000652cfdc0 bsp=e0000000652c9438
> [<a0000001003b5af0>] kobject_shadow_add+0x3b0/0x440
> sp=e0000000652cfdc0 bsp=e0000000652c93f0
> [<a0000001003b5bb0>] kobject_add+0x30/0x60
> sp=e0000000652cfdc0 bsp=e0000000652c93d0
> [<a000000100488240>] device_add+0x160/0xf40
> sp=e0000000652cfdc0 bsp=e0000000652c9358
> [<a00000010061af00>] netdev_register_sysfs+0xc0/0xe0
> sp=e0000000652cfdc0 bsp=e0000000652c9328
> [<a0000001006006c0>] register_netdevice+0x600/0x7e0
> sp=e0000000652cfdc0 bsp=e0000000652c92e8
> [<a000000100600910>] register_netdev+0x70/0xc0
> sp=e0000000652cfdd0 bsp=e0000000652c92c0
> [<a00000020018dd70>] e1000_probe+0x1710/0x1a00 [e1000]
> sp=e0000000652cfdd0 bsp=e0000000652c9258
> [<a0000001003d56c0>] pci_device_probe+0xc0/0x120
> sp=e0000000652cfde0 bsp=e0000000652c9218
> [<a00000010048dc60>] really_probe+0x1c0/0x300
> sp=e0000000652cfde0 bsp=e0000000652c91c8
> [<a00000010048df40>] driver_probe_device+0x1a0/0x1c0
> sp=e0000000652cfde0 bsp=e0000000652c9198
> [<a00000010048df90>] __device_attach+0x30/0x60
> sp=e0000000652cfde0 bsp=e0000000652c9170
> [<a00000010048c080>] bus_for_each_drv+0x80/0x120
> sp=e0000000652cfde0 bsp=e0000000652c9138
> [<a00000010048e0c0>] device_attach+0xa0/0x100
> sp=e0000000652cfe00 bsp=e0000000652c9110
> [<a00000010048bec0>] bus_attach_device+0x60/0xe0
> sp=e0000000652cfe00 bsp=e0000000652c90e0
> [<a000000100488a30>] device_add+0x950/0xf40
> sp=e0000000652cfe00 bsp=e0000000652c9068
> [<a0000001003ca360>] pci_bus_add_device+0x20/0x100
> sp=e0000000652cfe00 bsp=e0000000652c9040
> [<a0000001003ca490>] pci_bus_add_devices+0x50/0x320
> sp=e0000000652cfe00 bsp=e0000000652c9010
> [<a000000200081520>] shpchp_configure_device+0x460/0x4a0 [shpchp]
> sp=e0000000652cfe00 bsp=e0000000652c8fc0
> [<a00000020007e7c0>] board_added+0x720/0x8c0 [shpchp]
> sp=e0000000652cfe00 bsp=e0000000652c8f80
> [<a00000020007f280>] shpchp_enable_slot+0x920/0xa40 [shpchp]
> sp=e0000000652cfe10 bsp=e0000000652c8f30
> [<a000000200080a40>] shpchp_sysfs_enable_slot+0x120/0x220 [shpchp]
> sp=e0000000652cfe20 bsp=e0000000652c8ef8
> [<a00000020007d270>] enable_slot+0x90/0xc0 [shpchp]
> sp=e0000000652cfe20 bsp=e0000000652c8ed0
> [<a00000020002a760>] power_write_file+0x1e0/0x2a0 [pci_hotplug]
> sp=e0000000652cfe20 bsp=e0000000652c8ea0
> [<a000000200028100>] hotplug_slot_attr_store+0x60/0xa0 [pci_hotplug]
> sp=e0000000652cfe20 bsp=e0000000652c8e68
> [<a0000001001cf010>] sysfs_write_file+0x270/0x300
> sp=e0000000652cfe20 bsp=e0000000652c8e18
> [<a0000001001395b0>] vfs_write+0x1b0/0x300
> sp=e0000000652cfe20 bsp=e0000000652c8dc0
> [<a00000010013a1b0>] sys_write+0x70/0xe0
> sp=e0000000652cfe20 bsp=e0000000652c8d48
> [<a00000010000bc20>] ia64_ret_from_syscall+0x0/0x20
> sp=e0000000652cfe30 bsp=e0000000652c8d48
> [<a000000000010620>] __kernel_syscall_via_break+0x0/0x20
> sp=e0000000652d0000 bsp=e0000000652c8d48
>
> This error is caused by the race condition between dev_alloc_name()
> and unregistering net device. The dev_alloc_name() function checks
> dev_base list to find a suitable id. The net device is removed from
> the dev_base list when net device is unregistered. Those are done with
> rtnl lock held, so there is no problem. However, removing sysfs entry
> is delayed until netdev_run_todo() which is outside rtnl lock. Because
> of this, dev_alloc_name() can create a device name which is duplicated
> with the existing sysfs entry.
>
> The following patch fixes this by changing dev_alloc_name() function
> to check not only dev_base list but also todo list and snapshot list
> to find a suitable id. If some devices exists on the todo list or
> snapshot list, sysfs entries corresponding to them are not deleted
> yet.
>
> Thanks,
> Kenji Kaneshige

How about the following (untested), instead. It hold a removes the sysfs
entries earlier (on unregister_netdevice), but holds a kobject reference.
Then when todo runs the actual last put free happens.

---
net/core/dev.c | 10 ++++++----
net/core/net-sysfs.c | 8 +++++++-
2 files changed, 13 insertions(+), 5 deletions(-)

--- net-2.6.orig/net/core/dev.c 2007-05-11 09:10:10.000000000 -0700
+++ net-2.6/net/core/dev.c 2007-05-11 09:21:01.000000000 -0700
@@ -3245,7 +3245,6 @@ void netdev_run_todo(void)
continue;
}

- netdev_unregister_sysfs(dev);
dev->reg_state = NETREG_UNREGISTERED;

netdev_wait_allrefs(dev);
@@ -3256,11 +3255,11 @@ void netdev_run_todo(void)
BUG_TRAP(!dev->ip6_ptr);
BUG_TRAP(!dev->dn_ptr);

- /* It must be the very last action,
- * after this 'dev' may point to freed up memory.
- */
if (dev->destructor)
dev->destructor(dev);
+
+ /* Free network device */
+ kobject_put(&dev->dev.kobj);
}

out:
@@ -3411,6 +3410,9 @@ void unregister_netdevice(struct net_dev
/* Notifier chain MUST detach us from master device. */
BUG_TRAP(!dev->master);

+ /* Remove entries from sysfs */
+ netdev_unregister_sysfs(dev);
+
/* Finish processing unregister after unlock */
net_set_todo(dev);

--- net-2.6.orig/net/core/net-sysfs.c 2007-05-11 09:10:14.000000000 -0700
+++ net-2.6/net/core/net-sysfs.c 2007-05-11 09:14:45.000000000 -0700
@@ -456,9 +456,15 @@ static struct class net_class = {
#endif
};

+/* Delete sysfs entries but hold kobject reference until after all
+ * netdev references are gone.
+ */
void netdev_unregister_sysfs(struct net_device * net)
{
- device_del(&(net->dev));
+ struct device *dev = &(net->dev);
+
+ kobject_get(&dev->kobj);
+ device_del(dev);
}

/* Create sysfs entries for network device. */
-
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