PCI: kernel oops on access to pci proc file while hot-removal

I encountered the problem that /proc/bus/pci/XX/YY is not removed even
after the corresponding device is hot-removed, if the file is still
being opened. In addtion, accessing this file in this situation causes
kernel panic (see below).

Becasue the pci_proc_detach_device() doesn't call remove_proc_entry()
if struct proc_dir_entry->count > 1, access to /proc/bus/pci/XX/YY
would refer to struct pci_dev that was already freed.

Though I don't know why the check for proc_dir_entry->count was added,
I don't think it is needed. Removing this check fixes the problem.

Steps to reproduce
------------------
# cd /sys/bus/pci/slots/2/
# PROC_BUS_PCI_FILE=/proc/bus/pci/`awk -F: '{print $2"/"$3}' < address`.0
# sleep 10000 < $PROC_BUS_PCI_FILE &
# echo 0 > power
# while true; do cat $PROC_BUS_PCI_FILE > /dev/null; done

Oops Messages
-------------
BUG: unable to handle kernel NULL pointer dereference at 00000042
IP: [<c05c82d5>] pci_user_read_config_dword+0x65/0xa0
*pdpt = 000000002185e001 *pde = 0000000476a79067
Oops: 0000 [#1] SMP
last sysfs file: /sys/devices/pci0000:00/0000:00:1c.0/0000:10:00.0/local_cpus
Modules linked in: autofs4 sunrpc cpufreq_ondemand acpi_cpufreq ipv6 dm_mirror dm_region_hash dm_log dm_mod e1000e i2c_i801 i2c_core iTCO_wdt igb sg pcspkr dca iTCO_vendor_support ext4 mbcache jbd2 sd_mod crc_t10dif lpfc mptsas scsi_transport_fc mptscsih mptbase scsi_tgt scsi_transport_sas [last unloaded: microcode]

Pid: 2997, comm: cat Not tainted 2.6.34-kk #32 SB/PRIMEQUEST 1800E
EIP: 0060:[<c05c82d5>] EFLAGS: 00010046 CPU: 19
EIP is at pci_user_read_config_dword+0x65/0xa0
EAX: 00000002 EBX: e44f1800 ECX: e144df14 EDX: 155668c7
ESI: 00000087 EDI: 00000000 EBP: e144df40 ESP: e144df0c
 DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Process cat (pid: 2997, ti=e144c000 task=e26f2570 task.ti=e144c000)
Stack:
 c09ceac0 c0570f72 ffffffff 08c57000 00000000 00001000 e44f1800 c05d2404
<0> e144df40 00001000 00000000 00001000 08c57000 3093ae50 e420cb40 e358d5c0
<0> c05d2300 fffffffb c054984f e144df9c 00008000 08c57000 e358d5c0 00008000
Call Trace:
 [<c0570f72>] ? security_capable+0x22/0x30
 [<c05d2404>] ? proc_bus_pci_read+0x104/0x220
 [<c05d2300>] ? proc_bus_pci_read+0x0/0x220
 [<c054984f>] ? proc_reg_read+0x5f/0x90
 [<c05497f0>] ? proc_reg_read+0x0/0x90
 [<c050694d>] ? vfs_read+0x9d/0x190
 [<c04958f4>] ? audit_syscall_entry+0x204/0x230
 [<c0506a81>] ? sys_read+0x41/0x70
 [<c0402f1f>] ? sysenter_do_call+0x12/0x28
Code: b4 26 00 00 00 00 b8 20 88 b1 c0 c7 44 24 08 ff ff ff ff e8 3e 52 22 00 f6 83 24 04 00 00 20 75 34 8b 43 08 8d 4c 24 08 8b 53 1c <8b> 70 40 89 4c 24 04 89 f9 c7 04 24 04 00 00 00 ff 16 89 c6 f0
EIP: [<c05c82d5>] pci_user_read_config_dword+0x65/0xa0 SS:ESP 0068:e144df0c
CR2: 0000000000000042
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/proc.c

@@ -431,8 +431,6 @@ int pci_proc_detach_device(struct pci_dev *dev)
 	struct proc_dir_entry *e;
 
 	if ((e = dev->procent)) {
-		if (atomic_read(&e->count) > 1)
-			return -EBUSY;
 		remove_proc_entry(e->name, dev->bus->procdir);
 		dev->procent = NULL;
 	}