[PATCH] usb: fix number of mapped SG DMA entries

[Clemens Ladisch <clemens@ladisch.de>]

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 <clemens@ladisch.de>
---
 drivers/usb/core/hcd.c       |    5 ++---
 drivers/usb/host/ehci-q.c    |    2 +-
 drivers/usb/host/uhci-q.c    |    2 +-
 drivers/usb/host/whci/qset.c |    4 ++--
 drivers/usb/host/xhci-ring.c |    4 ++--
 include/linux/usb.h          |    1 +
 6 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 13222d3..179e364 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1412,11 +1412,10 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
 					ret = -EAGAIN;
 				else
 					urb->transfer_flags |= URB_DMA_MAP_SG;
+				urb->num_mapped_sgs = n;
-				if (n != urb->num_sgs) {
+				if (n != urb->num_sgs)
-					urb->num_sgs = n;
 					urb->transfer_flags |=
 							URB_DMA_SG_COMBINED;
-				}
 			} else if (urb->sg) {
 				struct scatterlist *sg = urb->sg;
 				urb->transfer_dma = dma_map_page(
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 4e4066c..fef1db3 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -647,7 +647,7 @@ qh_urb_transaction (
 	/*
 	 * 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);
diff --git a/drivers/usb/host/uhci-q.c b/drivers/usb/host/uhci-q.c
index f6ca80e..d2c6f5a 100644
--- a/drivers/usb/host/uhci-q.c
+++ b/drivers/usb/host/uhci-q.c
@@ -943,7 +943,7 @@ static int uhci_submit_common(struct uhci_hcd *uhci, struct urb *urb,
 	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);
diff --git a/drivers/usb/host/whci/qset.c b/drivers/usb/host/whci/qset.c
index d6e1754..a91712c 100644
--- a/drivers/usb/host/whci/qset.c
+++ b/drivers/usb/host/whci/qset.c
@@ -443,7 +443,7 @@ static int qset_add_urb_sg(struct whc *whc, struct whc_qset *qset, struct urb *u

 	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;
@@ -561,7 +561,7 @@ static int qset_add_urb_sg_linearize(struct whc *whc, struct whc_qset *qset,

 	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;
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 9f1d4b1..d28c586 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2561,7 +2561,7 @@ static unsigned int count_sg_trbs_needed(struct xhci_hcd *xhci, struct urb *urb)
 	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");
@@ -2745,7 +2745,7 @@ static int queue_bulk_sg_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
 		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));

diff --git a/include/linux/usb.h b/include/linux/usb.h
index d3d0c13..7503352 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1221,6 +1221,7 @@ struct urb {
 	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 */