When incoming packet qualifies for rx_copybreak, we copy the data to newly
allocated skb. We do not free/unmap the original buffer. At this point driver
assumes this buffer is unallocated. When enic_rq_alloc_buf() is called for
buffer allocation, it checks if buf->os_buf is NULL. If its not NULL that means
buffer can be re-used.

When vnic_rq_clean() is called for freeing all rq buffers, and if the
rx_copybreak reused buffer falls outside the used desc, we do not free the
buffer. The following trace is observer when dma-debug is enabled.

Fix is to walk through complete ring and clean if buffer is present.

[   40.555386] ------------[ cut here ]------------
[   40.555396] WARNING: CPU: 0 PID: 491 at lib/dma-debug.c:971 dma_debug_device_change+0x188/0x1f0()
[   40.555400] pci 0000:06:00.0: DMA-API: device driver has pending DMA allocations while released from device [count=4]
               One of leaked entries details: [device address=0x00000000ff4cc040] [size=9018 bytes] [mapped with DMA_FROM_DEVICE] [mapped as single]
[   40.555402] Modules linked in: nfsv3 nfs_acl rpcsec_gss_krb5 auth_rpcgss oid_registry nfsv4 dns_resolver coretemp intel_rapl iosf_mbi x86_pkg_temp_thermal intel_powerclamp kvm_intel kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 lrw joydev mousedev gf128mul hid_generic glue_helper mgag200 usbhid ttm hid drm_kms_helper drm ablk_helper syscopyarea sysfillrect sysimgblt i2c_algo_bit i2c_core iTCO_wdt cryptd mac_hid evdev pcspkr sb_edac edac_core tpm_tis iTCO_vendor_support ipmi_si wmi tpm ipmi_msghandler shpchp lpc_ich processor acpi_power_meter hwmon button ac sch_fq_codel nfs lockd grace sunrpc fscache sd_mod ehci_pci ehci_hcd megaraid_sas usbcore scsi_mod usb_common enic(-) crc32c_generic crc32c_intel btrfs xor raid6_pq ext4 crc16 mbcache jbd2
[   40.555467] CPU: 0 PID: 491 Comm: rmmod Not tainted 4.1.0-rc7-ARCH-01305-gf59b71f #118
[   40.555469] Hardware name: Cisco Systems Inc UCSB-B200-M4/UCSB-B200-M4, BIOS B200M4.2.2.2.23.061220140128 06/12/2014
[   40.555471]  0000000000000000 00000000e2f8a5b7 ffff880275f8bc48 ffffffff8158d6f0
[   40.555474]  0000000000000000 ffff880275f8bca0 ffff880275f8bc88 ffffffff8107b04a
[   40.555477]  ffff8802734e0000 0000000000000004 ffff8804763fb3c0 ffff88027600b650
[   40.555480] Call Trace:
[   40.555488]  [<ffffffff8158d6f0>] dump_stack+0x4f/0x7b
[   40.555492]  [<ffffffff8107b04a>] warn_slowpath_common+0x8a/0xc0
[   40.555494]  [<ffffffff8107b0d5>] warn_slowpath_fmt+0x55/0x70
[   40.555498]  [<ffffffff812fa408>] dma_debug_device_change+0x188/0x1f0
[   40.555503]  [<ffffffff8109aaef>] notifier_call_chain+0x4f/0x80
[   40.555506]  [<ffffffff8109aecb>] __blocking_notifier_call_chain+0x4b/0x70
[   40.555510]  [<ffffffff8109af06>] blocking_notifier_call_chain+0x16/0x20
[   40.555514]  [<ffffffff813f8066>] __device_release_driver+0xf6/0x120
[   40.555518]  [<ffffffff813f8b08>] driver_detach+0xc8/0xd0
[   40.555523]  [<ffffffff813f7c59>] bus_remove_driver+0x59/0xe0
[   40.555527]  [<ffffffff813f93a0>] driver_unregister+0x30/0x70
[   40.555534]  [<ffffffff8131532d>] pci_unregister_driver+0x2d/0xa0
[   40.555542]  [<ffffffffa0200ec2>] enic_cleanup_module+0x10/0x14e [enic]
[   40.555547]  [<ffffffff8110158f>] SyS_delete_module+0x1cf/0x280
[   40.555551]  [<ffffffff811e284e>] ? ____fput+0xe/0x10
[   40.555554]  [<ffffffff810980ec>] ? task_work_run+0xbc/0xf0
[   40.555558]  [<ffffffff815930ee>] system_call_fastpath+0x12/0x71
[   40.555561] ---[ end trace 4988cadc77c2b236 ]---
[   40.555562] Mapped at:
[   40.555563]  [<ffffffff812fa865>] debug_dma_map_page+0x95/0x150
[   40.555566]  [<ffffffffa01f4a88>] enic_rq_alloc_buf+0x1b8/0x360 [enic]
[   40.555570]  [<ffffffffa01f7658>] enic_open+0xf8/0x820 [enic]
[   40.555574]  [<ffffffff8148d50e>] __dev_open+0xce/0x150
[   40.555579]  [<ffffffff8148d851>] __dev_change_flags+0xa1/0x170

Signed-off-by: Govindarajulu Varadarajan <_govind@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>