NET: smsc95xx: don't use stack for async writes to the device

The set_multicast operation performs asynchronous writes to the
device, with some addresses pointing to the stack. Bad things may
happen, and this is trapped CONFIG_DMA_API_DEBUG:

[    5.237762] WARNING: at /build/buildd/linux-linaro-omap-2.6.38/lib/dma-debug.c:867 check_for_stack+0xd4/0x100()
[    5.237792] ehci-omap ehci-omap.0: DMA-API: device driver maps memory fromstack [addr=d9c77dec]
[    5.237792] Modules linked in: smsc95xx(+) usbnet twl6030_usb twl4030_pwrbutton leds_gpio omap_wdt omap2_mcspi
[    5.237854] [<c006d618>] (unwind_backtrace+0x0/0xf8) from [<c00a6a14>] (warn_slowpath_common+0x54/0x64)
[    5.237884] [<c00a6a14>] (warn_slowpath_common+0x54/0x64) from [<c00a6ab8>] (warn_slowpath_fmt+0x30/0x40)
[    5.237915] [<c00a6ab8>] (warn_slowpath_fmt+0x30/0x40) from [<c034e9d8>] (check_for_stack+0xd4/0x100)
[    5.237915] [<c034e9d8>] (check_for_stack+0xd4/0x100) from [<c034fea8>] (debug_dma_map_page+0xb4/0xdc)
[    5.237976] [<c034fea8>] (debug_dma_map_page+0xb4/0xdc) from [<c04242f0>] (map_urb_for_dma+0x26c/0x304)
[    5.237976] [<c04242f0>] (map_urb_for_dma+0x26c/0x304) from [<c0424594>] (usb_hcd_submit_urb+0x78/0x19c)
[    5.238037] [<c0424594>] (usb_hcd_submit_urb+0x78/0x19c) from [<bf049c5c>] (smsc95xx_write_reg_async+0xb4/0x130 [smsc95xx])
[    5.238067] [<bf049c5c>] (smsc95xx_write_reg_async+0xb4/0x130 [smsc95xx]) from [<bf049dd4>] (smsc95xx_set_multicast+0xfc/0x148 [smsc95xx])
[    5.238098] [<bf049dd4>] (smsc95xx_set_multicast+0xfc/0x148 [smsc95xx]) from [<bf04a118>] (smsc95xx_reset+0x2f8/0x68c [smsc95xx])
[    5.238128] [<bf04a118>] (smsc95xx_reset+0x2f8/0x68c [smsc95xx]) from [<bf04a8cc>] (smsc95xx_bind+0xcc/0x188 [smsc95xx])
[    5.238159] [<bf04a8cc>] (smsc95xx_bind+0xcc/0x188 [smsc95xx]) from [<bf03ef1c>] (usbnet_probe+0x204/0x4c4 [usbnet])
[    5.238220] [<bf03ef1c>] (usbnet_probe+0x204/0x4c4 [usbnet]) from [<c0429078>] (usb_probe_interface+0xe4/0x1c4)
[    5.238250] [<c0429078>] (usb_probe_interface+0xe4/0x1c4) from [<c03a8770>] (really_probe+0x64/0x160)
[    5.238250] [<c03a8770>] (really_probe+0x64/0x160) from [<c03a8a30>] (driver_probe_device+0x48/0x60)
[    5.238281] [<c03a8a30>] (driver_probe_device+0x48/0x60) from [<c03a8ad4>] (__driver_attach+0x8c/0x90)
[    5.238311] [<c03a8ad4>] (__driver_attach+0x8c/0x90) from [<c03a7b24>] (bus_for_each_dev+0x50/0x7c)
[    5.238311] [<c03a7b24>] (bus_for_each_dev+0x50/0x7c) from [<c03a82ec>] (bus_add_driver+0x190/0x250)
[    5.238311] [<c03a82ec>] (bus_add_driver+0x190/0x250) from [<c03a8cf8>] (driver_register+0x78/0x13c)
[    5.238433] [<c03a8cf8>] (driver_register+0x78/0x13c) from [<c0428040>] (usb_register_driver+0x78/0x13c)
[    5.238464] [<c0428040>] (usb_register_driver+0x78/0x13c) from [<c005b680>] (do_one_initcall+0x34/0x188)
[    5.238494] [<c005b680>] (do_one_initcall+0x34/0x188) from [<c00e11f0>] (sys_init_module+0xb0/0x1c0)
[    5.238525] [<c00e11f0>] (sys_init_module+0xb0/0x1c0) from [<c0065c40>] (ret_fast_syscall+0x0/0x30)

Move the two offenders to the private structure which is kmalloc-ed,
and thus safe.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Steve Glendinning <steve.glendinning@smsc.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/smsc95xx.c

@@ -49,6 +49,8 @@
 
 struct smsc95xx_priv {
 	u32 mac_cr;
+	u32 hash_hi;
+	u32 hash_lo;
 	spinlock_t mac_cr_lock;
 	bool use_tx_csum;
 	bool use_rx_csum;
@@ -370,10 +372,11 @@ static void smsc95xx_set_multicast(struct net_device *netdev)
 {
 	struct usbnet *dev = netdev_priv(netdev);
 	struct smsc95xx_priv *pdata = (struct smsc95xx_priv *)(dev->data[0]);
-	u32 hash_hi = 0;
-	u32 hash_lo = 0;
 	unsigned long flags;
 
+	pdata->hash_hi = 0;
+	pdata->hash_lo = 0;
+
 	spin_lock_irqsave(&pdata->mac_cr_lock, flags);
 
 	if (dev->net->flags & IFF_PROMISC) {
@@ -394,13 +397,13 @@ static void smsc95xx_set_multicast(struct net_device *netdev)
 			u32 bitnum = smsc95xx_hash(ha->addr);
 			u32 mask = 0x01 << (bitnum & 0x1F);
 			if (bitnum & 0x20)
-				hash_hi |= mask;
+				pdata->hash_hi |= mask;
 			else
-				hash_lo |= mask;
+				pdata->hash_lo |= mask;
 		}
 
 		netif_dbg(dev, drv, dev->net, "HASHH=0x%08X, HASHL=0x%08X\n",
-				   hash_hi, hash_lo);
+				   pdata->hash_hi, pdata->hash_lo);
 	} else {
 		netif_dbg(dev, drv, dev->net, "receive own packets only\n");
 		pdata->mac_cr &=
@@ -410,8 +413,8 @@ static void smsc95xx_set_multicast(struct net_device *netdev)
 	spin_unlock_irqrestore(&pdata->mac_cr_lock, flags);
 
 	/* Initiate async writes, as we can't wait for completion here */
-	smsc95xx_write_reg_async(dev, HASHH, &hash_hi);
-	smsc95xx_write_reg_async(dev, HASHL, &hash_lo);
+	smsc95xx_write_reg_async(dev, HASHH, &pdata->hash_hi);
+	smsc95xx_write_reg_async(dev, HASHL, &pdata->hash_lo);
 	smsc95xx_write_reg_async(dev, MAC_CR, &pdata->mac_cr);
 }