forcedeth: Do a dma_mapping_error check after skb_frag_dma_map

This backtrace was recently reported on a 3.9 kernel:

Actual results: from syslog /var/log/messsages:
kernel: [17539.340285] ------------[ cut here ]------------
kernel: [17539.341012] WARNING: at lib/dma-debug.c:937 check_unmap+0x493/0x960()
kernel: [17539.341012] Hardware name: MS-7125
kernel: [17539.341012] forcedeth 0000:00:0a.0: DMA-API: device driver failed to
check map error[device address=0x0000000013c88000] [size=544 bytes] [mapped as
page]
kernel: [17539.341012] Modules linked in: fuse ebtable_nat ipt_MASQUERADE
nf_conntrack_netbios_ns nf_conntrack_broadcast ip6table_nat nf_nat_ipv6
ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat
nf_nat_ipv4 nf_nat iptable_mangle nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack
nf_conntrack bnep bluetooth rfkill ebtable_filter ebtables ip6table_filter
ip6_tables snd_hda_codec_hdmi snd_cmipci snd_mpu401_uart snd_hda_intel
snd_intel8x0 snd_opl3_lib snd_ac97_codec gameport snd_hda_codec snd_rawmidi
ac97_bus snd_hwdep snd_seq snd_seq_device snd_pcm snd_page_alloc snd_timer snd
k8temp soundcore serio_raw i2c_nforce2 forcedeth ata_generic pata_acpi nouveau
video mxm_wmi wmi i2c_algo_bit drm_kms_helper ttm drm i2c_core sata_sil pata_amd
sata_nv uinput
kernel: [17539.341012] Pid: 17340, comm: sshd Not tainted
3.9.0-0.rc4.git0.1.fc19.i686.PAE #1
kernel: [17539.341012] Call Trace:
kernel: [17539.341012]  [<c045573c>] warn_slowpath_common+0x6c/0xa0
kernel: [17539.341012]  [<c0701953>] ? check_unmap+0x493/0x960
kernel: [17539.341012]  [<c0701953>] ? check_unmap+0x493/0x960
kernel: [17539.341012]  [<c04557a3>] warn_slowpath_fmt+0x33/0x40
kernel: [17539.341012]  [<c0701953>] check_unmap+0x493/0x960
kernel: [17539.341012]  [<c049238f>] ? sched_clock_cpu+0xdf/0x150
kernel: [17539.341012]  [<c0701e87>] debug_dma_unmap_page+0x67/0x70
kernel: [17539.341012]  [<f7eae8f2>] nv_unmap_txskb.isra.32+0x92/0x100

Its pretty plainly the result of an skb fragment getting unmapped without having
its initial mapping operation checked for errors.  This patch corrects that.
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/nvidia/forcedeth.c

@@ -2200,6 +2200,7 @@ static netdev_tx_t nv_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct ring_desc *start_tx;
 	struct ring_desc *prev_tx;
 	struct nv_skb_map *prev_tx_ctx;
+	struct nv_skb_map *tmp_tx_ctx = NULL, *start_tx_ctx = NULL;
 	unsigned long flags;
 
 	/* add fragments to entries count */
@@ -2261,12 +2262,31 @@ static netdev_tx_t nv_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		do {
 			prev_tx = put_tx;
 			prev_tx_ctx = np->put_tx_ctx;
+			if (!start_tx_ctx)
+				start_tx_ctx = tmp_tx_ctx = np->put_tx_ctx;
+
 			bcnt = (frag_size > NV_TX2_TSO_MAX_SIZE) ? NV_TX2_TSO_MAX_SIZE : frag_size;
 			np->put_tx_ctx->dma = skb_frag_dma_map(
 							&np->pci_dev->dev,
 							frag, offset,
 							bcnt,
 							DMA_TO_DEVICE);
+			if (dma_mapping_error(&np->pci_dev->dev, np->put_tx_ctx->dma)) {
+
+				/* Unwind the mapped fragments */
+				do {
+					nv_unmap_txskb(np, start_tx_ctx);
+					if (unlikely(tmp_tx_ctx++ == np->last_tx_ctx))
+						tmp_tx_ctx = np->first_tx_ctx;
+				} while (tmp_tx_ctx != np->put_tx_ctx);
+				kfree_skb(skb);
+				np->put_tx_ctx = start_tx_ctx;
+				u64_stats_update_begin(&np->swstats_tx_syncp);
+				np->stat_tx_dropped++;
+				u64_stats_update_end(&np->swstats_tx_syncp);
+				return NETDEV_TX_OK;
+			}
+
 			np->put_tx_ctx->dma_len = bcnt;
 			np->put_tx_ctx->dma_single = 0;
 			put_tx->buf = cpu_to_le32(np->put_tx_ctx->dma);
@@ -2327,7 +2347,8 @@ static netdev_tx_t nv_start_xmit_optimized(struct sk_buff *skb,
 	struct ring_desc_ex *start_tx;
 	struct ring_desc_ex *prev_tx;
 	struct nv_skb_map *prev_tx_ctx;
-	struct nv_skb_map *start_tx_ctx;
+	struct nv_skb_map *start_tx_ctx = NULL;
+	struct nv_skb_map *tmp_tx_ctx = NULL;
 	unsigned long flags;
 
 	/* add fragments to entries count */
@@ -2392,11 +2413,29 @@ static netdev_tx_t nv_start_xmit_optimized(struct sk_buff *skb,
 			prev_tx = put_tx;
 			prev_tx_ctx = np->put_tx_ctx;
 			bcnt = (frag_size > NV_TX2_TSO_MAX_SIZE) ? NV_TX2_TSO_MAX_SIZE : frag_size;
+			if (!start_tx_ctx)
+				start_tx_ctx = tmp_tx_ctx = np->put_tx_ctx;
 			np->put_tx_ctx->dma = skb_frag_dma_map(
 							&np->pci_dev->dev,
 							frag, offset,
 							bcnt,
 							DMA_TO_DEVICE);
+
+			if (dma_mapping_error(&np->pci_dev->dev, np->put_tx_ctx->dma)) {
+
+				/* Unwind the mapped fragments */
+				do {
+					nv_unmap_txskb(np, start_tx_ctx);
+					if (unlikely(tmp_tx_ctx++ == np->last_tx_ctx))
+						tmp_tx_ctx = np->first_tx_ctx;
+				} while (tmp_tx_ctx != np->put_tx_ctx);
+				kfree_skb(skb);
+				np->put_tx_ctx = start_tx_ctx;
+				u64_stats_update_begin(&np->swstats_tx_syncp);
+				np->stat_tx_dropped++;
+				u64_stats_update_end(&np->swstats_tx_syncp);
+				return NETDEV_TX_OK;
+			}
 			np->put_tx_ctx->dma_len = bcnt;
 			np->put_tx_ctx->dma_single = 0;
 			put_tx->bufhigh = cpu_to_le32(dma_high(np->put_tx_ctx->dma));