3c59x: avoid panic in boomerang_start_xmit when finding page address:

This bug was reported on a very old kernel (RHEL6, 2.6.32-491.el6):

BUG: unable to handle kernel paging request at 00800000
IP: [<c04107b5>] nommu_map_page+0x15/0x110
*pdpt = 000000003454f001 *pde = 000000003f03d067
Oops: 0000 [#1] SMP
last sysfs file: /sys/devices/system/cpu/online
Modules linked in: nfsd lockd nfs_acl auth_rpcgss sunrpc exportfs p4_clockmod
ipv6 ppdev parport_pc parport microcode iTCO_wdt iTCO_vendor_support 3c59x mii
dcdbas serio_raw snd_intel8x0 snd_ac97_codec ac97_bus snd_seq snd_seq_device
snd_pcm snd_timer snd soundcore snd_page_alloc i2c_i801 sg lpc_ich mfd_core ext4
jbd2 mbcache sr_mod cdrom sd_mod crc_t10dif pata_acpi ata_generic ata_piix
radeon ttm drm_kms_helper drm i2c_algo_bit i2c_core dm_mirror dm_region_hash
dm_log dm_mod [last unloaded: mperf]

Pid: 4219, comm: nfsd Not tainted 2.6.32-491.el6.i686 #1 Dell Computer
Corporation OptiPlex GX240               /OptiPlex GX240
EIP: 0060:[<c04107b5>] EFLAGS: 00010246 CPU: 0
EIP is at nommu_map_page+0x15/0x110
EAX: 00000000 EBX: c0a83480 ECX: 00000000 EDX: 00800000
ESI: 00000000 EDI: f70e7860 EBP: e2d09b54 ESP: e2d09b24
 DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Process nfsd (pid: 4219, ti=e2d08000 task=e2ceaaa0 task.ti=e2d08000)
Stack:
 00000056 00000000 0000000e c65efd38 00000020 00000296 00000206 00000206
<0> c050c850 c0a83480 e2cef154 00000001 e2d09ba8 f8fcd585 00000510 00000001
<0> 00000000 00000000 f5172200 f8fdac00 0039ef8c f5277020 f70e7860 00000510
Call Trace:
 [<c050c850>] ? page_address+0xd0/0xe0
 [<f8fcd585>] ? boomerang_start_xmit+0x3b5/0x520 [3c59x]
 [<c07b2975>] ? dev_hard_start_xmit+0xe5/0x400
 [<f9182b00>] ? ip6_output_finish+0x0/0xf0 [ipv6]
 [<c07ca053>] ? sch_direct_xmit+0x113/0x180
 [<c07d5588>] ? nf_hook_slow+0x68/0x120
 [<c07b2ea5>] ? dev_queue_xmit+0x1b5/0x290
 [<f9182b6d>] ? ip6_output_finish+0x6d/0xf0 [ipv6]
 [<f9184cb8>] ? ip6_xmit+0x3e8/0x490 [ipv6]
 [<f91ab9f9>] ? inet6_csk_xmit+0x289/0x2f0 [ipv6]
 [<c07f6451>] ? tcp_transmit_skb+0x431/0x7f0
 [<c07a403f>] ? __alloc_skb+0x4f/0x140
 [<c07f85a2>] ? tcp_write_xmit+0x1c2/0xa50
 [<c07f90b1>] ? __tcp_push_pending_frames+0x31/0xe0
 [<c07ea47a>] ? tcp_sendpage+0x44a/0x4b0
 [<c07ea030>] ? tcp_sendpage+0x0/0x4b0
 [<c079be1e>] ? kernel_sendpage+0x4e/0x90
 [<f8457bb9>] ? svc_send_common+0xc9/0x120 [sunrpc]
 [<f8457c85>] ? svc_sendto+0x75/0x1f0 [sunrpc]
 [<c060d0d9>] ? _atomic_dec_and_lock+0x59/0x90
 [<f87d55d0>] ? nfs3svc_encode_readres+0x0/0xc0 [nfsd]
 [<f845876d>] ? svc_authorise+0x2d/0x40 [sunrpc]
 [<f87d4410>] ? nfs3svc_release_fhandle+0x0/0x10 [nfsd]
 [<f8455721>] ? svc_process_common+0xf1/0x5a0 [sunrpc]
 [<f8457e86>] ? svc_tcp_sendto+0x36/0xa0 [sunrpc]
 [<f8461778>] ? svc_send+0x98/0xd0 [sunrpc]
 [<f87c698c>] ? nfsd+0xac/0x140 [nfsd]
 [<c04470e0>] ? complete+0x40/0x60
 [<f87c68e0>] ? nfsd+0x0/0x140 [nfsd]
 [<c04802ac>] ? kthread+0x7c/0xa0
 [<c0480230>] ? kthread+0x0/0xa0
 [<c0409f9f>] ? kernel_thread_helper+0x7/0x10
Code: 8d b6 00 00 00 00 eb f8 8d b4 26 00 00 00 00 8d bc 27 00 00 00 00 55 89 e5
83 ec 30 89 75 f8 31 f6 89 7d fc 89 c7 89 c8 89 5d f4 <8b> 1a 8b 4d 08 c1 eb 19
c1 e3 04 8b 9b c0 29 c7 c0 83 e3 fc 29

But the problem seems to still exist upstream.  It seems on 32 bit kernels
page_address() can reutrn a NULL value in some circumstances, and the
pci_map_single api isn't prepared to handle that (on this system it results in a
bogus pointer deference in nommu_map_page.

The fix is pretty easy, if we convert the 3c59x driver to use the more
convieient skb_frag_dma_map api we don't need to find the virtual address of the
page at all, and page gets mapped to the hardware properly.  Verified to fix the
problem as described by the reporter.

Applies to the net tree

Change Notes:

v2) Converted PCI_DMA_TODEVICE to DMA_TO_DEVICE.  Thanks Dave!

v3) Actually Run git commit after making changes to v2 :)

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: klassert@mathematik.tu-chemnitz.de
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>