ibmveth: Fix rx pool deactivate oops

This fixes the following oops which can occur when trying to deallocate
receive buffer pools using sysfs with the ibmveth driver.

NIP: d00000000024f954 LR: d00000000024fa58 CTR: c0000000000d7478
REGS: c00000000ffef9f0 TRAP: 0300   Not tainted  (2.6.22-ppc64)
MSR: 8000000000009032 <EE,ME,IR,DR>  CR: 24242442  XER: 00000010
DAR: 00000000000007f0, DSISR: 0000000042000000
TASK = c000000002f91360[2967] 'bash' THREAD: c00000001398c000 CPU: 2
GPR00: 0000000000000000 c00000000ffefc70 d000000000262d30 c00000001c4087a0
GPR04: 00000003000000fe 0000000000000000 000000000000000f c000000000579d80
GPR08: 0000000000365688 c00000001c408998 00000000000007f0 0000000000000000
GPR12: d000000000251e88 c000000000579d80 00000000200957ec 0000000000000000
GPR16: 00000000100b8808 00000000100feb30 0000000000000000 0000000010084828
GPR20: 0000000000000000 000000001014d4d0 0000000000000010 c00000000ffefeb0
GPR24: c00000001c408000 0000000000000000 c00000001c408000 00000000ffffb054
GPR28: 00000000000000fe 0000000000000003 d000000000262700 c00000001c4087a0
NIP [d00000000024f954] .ibmveth_remove_buffer_from_pool+0x38/0x108 [ibmveth]
LR [d00000000024fa58] .ibmveth_rxq_harvest_buffer+0x34/0x78 [ibmveth]
Call Trace:
[c00000000ffefc70] [c0000000000280a8] .dma_iommu_unmap_single+0x14/0x28 (unreliable)
[c00000000ffefd00] [d00000000024fa58] .ibmveth_rxq_harvest_buffer+0x34/0x78 [ibmveth]
[c00000000ffefd80] [d000000000250e40] .ibmveth_poll+0xd8/0x434 [ibmveth]
[c00000000ffefe40] [c00000000032da8c] .net_rx_action+0xdc/0x248
[c00000000ffefef0] [c000000000068b4c] .__do_softirq+0xa8/0x164
[c00000000ffeff90] [c00000000002789c] .call_do_softirq+0x14/0x24
[c00000001398f6f0] [c00000000000c04c] .do_softirq+0x68/0xac
[c00000001398f780] [c000000000068ca0] .irq_exit+0x54/0x6c
[c00000001398f800] [c00000000000c8e4] .do_IRQ+0x170/0x1ac
[c00000001398f890] [c000000000004790] hardware_interrupt_entry+0x18/0x1c
   Exception: 501 at .plpar_hcall_norets+0x24/0x94
    LR = .veth_pool_store+0x15c/0x298 [ibmveth]
[c00000001398fb80] [d000000000250b2c] .veth_pool_store+0x5c/0x298 [ibmveth] (unreliable)
[c00000001398fc30] [c000000000145530] .sysfs_write_file+0x140/0x1d8
[c00000001398fcf0] [c0000000000de89c] .vfs_write+0x120/0x208
[c00000001398fd90] [c0000000000df2c8] .sys_write+0x4c/0x8c
[c00000001398fe30] [c0000000000086ac] syscall_exit+0x0/0x40
Instruction dump:
fba1ffe8 fbe1fff8 789d0022 f8010010 f821ff71 789c0020 1d3d00a8 7b8a1f24
38000000 7c7f1b78 7d291a14 e9690128 <7c0a592a> e8030000 e9690120 80a90100

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>