Subject: [BUG][PATCH] Fix race condition about network device name allocation

From: Kenji Kaneshige <[email-masked]>
Date: Fri, 11 May 2007 14:40:45 +0900

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

---
Fix the race condition between dev_alloc_name() and net device
unregistration.

dev_alloc_name checks `dev_base' list to find a suitable ID. On the
other hand, net devices are removed from that list on net device
unregistration. Both of them are done with holding rtnl lock. However,
removing sysfs entry is delayed until netdev_run_todo(), which doesn't
acquire rtnl lock. Therefore, on dev_alloc_name(), device name could
conflict with the device, which is unregistered, but its sysfs entry
still exist.

To fix this bug, change dev_alloc_name to check not only `dev_base'
list but also todo list and snapshot list.

Signed-off-by: Kenji Kaneshige <[email-masked]>

---
 net/core/dev.c |   48 ++++++++++++++++++++++++++++++++++++++----------
 1 files changed, 38 insertions(+), 10 deletions(-)

Index: linux-2.6.21/net/core/dev.c
===================================================================
--- linux-2.6.21.orig/net/core/dev.c
+++ linux-2.6.21/net/core/dev.c
@@ -218,6 +218,11 @@ extern void netdev_unregister_sysfs(stru
 #define	netdev_unregister_sysfs(dev)	do { } while(0)
 #endif
 
+/* Delayed registration/unregisteration */
+static DEFINE_SPINLOCK(net_todo_list_lock);
+static LIST_HEAD(net_todo_list);
+static LIST_HEAD(net_todo_snapshot_list);
+
 
 /*******************************************************************************
 
@@ -702,7 +707,32 @@ int dev_alloc_name(struct net_device *de
 				set_bit(i, inuse);
 		}
 
+		spin_lock(&net_todo_list_lock);
+		list_for_each_entry(d, &net_todo_list, todo_list) {
+			if (!sscanf(d->name, name, &i))
+				continue;
+			if (i < 0 || i >= max_netdevices)
+				continue;
+
+			/*  avoid cases where sscanf is not exact inverse of printf */
+			snprintf(buf, sizeof(buf), name, i);
+			if (!strncmp(buf, d->name, IFNAMSIZ))
+				set_bit(i, inuse);
+		}
+		list_for_each_entry(d, &net_todo_snapshot_list, todo_list) {
+			if (!sscanf(d->name, name, &i))
+				continue;
+			if (i < 0 || i >= max_netdevices)
+				continue;
+
+			/*  avoid cases where sscanf is not exact inverse of printf */
+			snprintf(buf, sizeof(buf), name, i);
+			if (!strncmp(buf, d->name, IFNAMSIZ))
+				set_bit(i, inuse);
+		}
 		i = find_first_zero_bit(inuse, max_netdevices);
+		spin_unlock(&net_todo_list_lock);
+
 		free_page((unsigned long) inuse);
 	}
 
@@ -2843,10 +2873,6 @@ static int dev_new_index(void)
 
 static int dev_boot_phase = 1;
 
-/* Delayed registration/unregisteration */
-static DEFINE_SPINLOCK(net_todo_list_lock);
-static struct list_head net_todo_list = LIST_HEAD_INIT(net_todo_list);
-
 static inline void net_set_todo(struct net_device *dev)
 {
 	spin_lock(&net_todo_list_lock);
@@ -3105,8 +3131,6 @@ static void netdev_wait_allrefs(struct n
 static DEFINE_MUTEX(net_todo_run_mutex);
 void netdev_run_todo(void)
 {
-	struct list_head list;
-
 	/* Need to guard against multiple cpu's getting out of order. */
 	mutex_lock(&net_todo_run_mutex);
 
@@ -3120,13 +3144,13 @@ void netdev_run_todo(void)
 
 	/* Snapshot list, allow later requests */
 	spin_lock(&net_todo_list_lock);
-	list_replace_init(&net_todo_list, &list);
+	list_replace_init(&net_todo_list, &net_todo_snapshot_list);
 	spin_unlock(&net_todo_list_lock);
 
-	while (!list_empty(&list)) {
+	while (!list_empty(&net_todo_snapshot_list)) {
 		struct net_device *dev
-			= list_entry(list.next, struct net_device, todo_list);
-		list_del(&dev->todo_list);
+			= list_entry(net_todo_snapshot_list.next,
+				     struct net_device, todo_list);
 
 		if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
 			printk(KERN_ERR "network todo '%s' but state %d\n",
@@ -3146,6 +3170,10 @@ void netdev_run_todo(void)
 		BUG_TRAP(!dev->ip6_ptr);
 		BUG_TRAP(!dev->dn_ptr);
 
+		spin_lock(&net_todo_list_lock);
+		list_del(&dev->todo_list);
+		spin_unlock(&net_todo_list_lock);
+
 		/* It must be the very last action,
 		 * after this 'dev' may point to freed up memory.
 		 */