usb: fix number of mapped SG DMA entries

Add a new field num_mapped_sgs to struct urb so that we have a place to
store the number of mapped entries and can also retain the original
value of entries in num_sgs. Previously, usb_hcd_map_urb_for_dma()
would overwrite this with the number of mapped entries, which would
break dma_unmap_sg() because it requires the original number of entries.

This fixes warnings like the following when using USB storage devices:
------------[ cut here ]------------
WARNING: at lib/dma-debug.c:902 check_unmap+0x4e4/0x695()
ehci_hcd 0000:00:12.2: DMA-API: device driver frees DMA sg list with different entry count [map count=4] [unmap count=1]
Modules linked in: ohci_hcd ehci_hcd
Pid: 0, comm: kworker/0:1 Not tainted 3.2.0-rc2+ #319
Call Trace:
<IRQ> [<ffffffff81036d3b>] warn_slowpath_common+0x80/0x98
[<ffffffff81036de7>] warn_slowpath_fmt+0x41/0x43
[<ffffffff811fa5ae>] check_unmap+0x4e4/0x695
[<ffffffff8105e92c>] ? trace_hardirqs_off+0xd/0xf
[<ffffffff8147208b>] ? _raw_spin_unlock_irqrestore+0x33/0x50
[<ffffffff811fa84a>] debug_dma_unmap_sg+0xeb/0x117
[<ffffffff8137b02f>] usb_hcd_unmap_urb_for_dma+0x71/0x188
[<ffffffff8137b166>] unmap_urb_for_dma+0x20/0x22
[<ffffffff8137b1c5>] usb_hcd_giveback_urb+0x5d/0xc0
[<ffffffffa0000d02>] ehci_urb_done+0xf7/0x10c [ehci_hcd]
[<ffffffffa0001140>] qh_completions+0x429/0x4bd [ehci_hcd]
[<ffffffffa000340a>] ehci_work+0x95/0x9c0 [ehci_hcd]
...
---[ end trace f29ac88a5a48c580 ]---
Mapped at:
[<ffffffff811faac4>] debug_dma_map_sg+0x45/0x139
[<ffffffff8137bc0b>] usb_hcd_map_urb_for_dma+0x22e/0x478
[<ffffffff8137c494>] usb_hcd_submit_urb+0x63f/0x6fa
[<ffffffff8137d01c>] usb_submit_urb+0x2c7/0x2de
[<ffffffff8137dcd4>] usb_sg_wait+0x55/0x161

Signed-off-by: Clemens Ladisch <[e-mail]>
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/hcd.c

···
 					ret = -EAGAIN;
 				else
 					urb->transfer_flags |= URB_DMA_MAP_SG;
-				if (n != urb->num_sgs) {
-					urb->num_sgs = n;
+				urb->num_mapped_sgs = n;
+				if (n != urb->num_sgs)
 					urb->transfer_flags |=
 							URB_DMA_SG_COMBINED;
-				}
 			} else if (urb->sg) {
 				struct scatterlist *sg = urb->sg;
 				urb->transfer_dma = dma_map_page(

drivers/usb/host/ehci-q.c

···
 	/*
 	 * data transfer stage:  buffer setup
 	 */
-	i = urb->num_sgs;
+	i = urb->num_mapped_sgs;
 	if (len > 0 && i > 0) {
 		sg = urb->sg;
 		buf = sg_dma_address(sg);

drivers/usb/host/uhci-q.c

···
 	if (usb_pipein(urb->pipe))
 		status |= TD_CTRL_SPD;
 
-	i = urb->num_sgs;
+	i = urb->num_mapped_sgs;
 	if (len > 0 && i > 0) {
 		sg = urb->sg;
 		data = sg_dma_address(sg);

drivers/usb/host/whci/qset.c

···
 
 	remaining = urb->transfer_buffer_length;
 
-	for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+	for_each_sg(urb->sg, sg, urb->num_mapped_sgs, i) {
 		dma_addr_t dma_addr;
 		size_t dma_remaining;
 		dma_addr_t sp, ep;
···
 
 	remaining = urb->transfer_buffer_length;
 
-	for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+	for_each_sg(urb->sg, sg, urb->num_mapped_sgs, i) {
 		size_t len;
 		size_t sg_remaining;
 		void *orig;

drivers/usb/host/xhci-ring.c

···
 	struct scatterlist *sg;
 
 	sg = NULL;
-	num_sgs = urb->num_sgs;
+	num_sgs = urb->num_mapped_sgs;
 	temp = urb->transfer_buffer_length;
 
 	xhci_dbg(xhci, "count sg list trbs: \n");
···
 		return -EINVAL;
 
 	num_trbs = count_sg_trbs_needed(xhci, urb);
-	num_sgs = urb->num_sgs;
+	num_sgs = urb->num_mapped_sgs;
 	total_packet_count = roundup(urb->transfer_buffer_length,
 			usb_endpoint_maxp(&urb->ep->desc));
 

include/linux/usb.h

···
 	void *transfer_buffer;		/* (in) associated data buffer */
 	dma_addr_t transfer_dma;	/* (in) dma addr for transfer_buffer */
 	struct scatterlist *sg;		/* (in) scatter gather buffer list */
+	int num_mapped_sgs;		/* (internal) mapped sg entries */
 	int num_sgs;			/* (in) number of entries in the sg list */
 	u32 transfer_buffer_length;	/* (in) data buffer length */
 	u32 actual_length;		/* (return) actual transfer length */