USB: fix usbmon and DMA mapping for scatter-gather URBs

This patch (as1368) fixes a rather obscure bug in usbmon: When tracing
URBs sent by the scatter-gather library, it accesses the data buffers
while they are still mapped for DMA.

The solution is to move the mapping and unmapping out of the s-g
library and into the usual place in hcd.c.  This requires the addition
of new URB flag bits to describe the kind of mapping needed, since we
have to call dma_map_sg() if the HCD supports native scatter-gather
operation and dma_map_page() if it doesn't.  The nice thing about
having the new flags is that they simplify the testing for unmapping.

The patch removes the only caller of usb_buffer_[un]map_sg(), so those
functions are #if'ed out.  A later patch will remove them entirely.

As a result of this change, urb->sg will be set in situations where
it wasn't set previously.  Hence the xhci and whci drivers are
adjusted to test urb->num_sgs instead, which retains its original
meaning and is nonzero only when the HCD has to handle a scatterlist.

Finally, even when a submission error occurs we don't want to hand
URBs to usbmon before they are unmapped.  The submission path is
rearranged so that map_urb_for_dma() is called only for non-root-hub
URBs and unmap_urb_for_dma() is called immediately after a submission
error.  This simplifies the error handling.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 2 insertions, 4 deletions

diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c
index ddf7f9a1b336..8a7968df278f 100644
--- a/drivers/usb/mon/mon_bin.c
+++ b/drivers/usb/mon/mon_bin.c
@@ -416,7 +416,7 @@ static unsigned int mon_bin_get_data(const struct mon_reader_bin *rp,
 
         } else {
                 /* If IOMMU coalescing occurred, we cannot trust sg_page */
-                if (urb->sg->nents != urb->num_sgs) {
+                if (urb->transfer_flags & URB_DMA_SG_COMBINED) {
                         *flag = 'D';
                         return length;
                 }
diff --git a/drivers/usb/mon/mon_text.c b/drivers/usb/mon/mon_text.c
index 4d0be130f49b..d56260280f54 100644
--- a/drivers/usb/mon/mon_text.c
+++ b/drivers/usb/mon/mon_text.c
@@ -161,9 +161,7 @@ static inline char mon_text_get_data(struct mon_event_text *ep, struct urb *urb,
         } else {
                 struct scatterlist *sg = urb->sg->sg;
 
-                /* If IOMMU coalescing occurred, we cannot trust sg_page */
-                if (urb->sg->nents != urb->num_sgs ||
-                                PageHighMem(sg_page(sg)))
+                if (PageHighMem(sg_page(sg)))
                         return 'D';
 
                 /* For the text interface we copy only the first sg buffer */