usb-storage: Revert commit 747668d ("usb-storage: Set virt_boundary_mask to avoid SG overflows")

Commit 747668d ("usb-storage: Set virt_boundary_mask to avoid SG
overflows") attempted to solve a problem involving scatter-gather I/O
and USB/IP by setting the virt_boundary_mask for mass-storage devices.

However, it now turns out that this interacts badly with commit
09324d3 ("block: force an unlimited segment size on queues with a
virt boundary"), which was added later.  A typical error message is:

	ehci-pci 0000:00:13.2: swiotlb buffer is full (sz: 327680 bytes),
	total 32768 (slots), used 97 (slots)

There is no longer any reason to keep the virt_boundary_mask setting
for usb-storage.  It was needed in the first place only for handling
devices with a block size smaller than the maxpacket size and where
the host controller was not capable of fully general scatter-gather
operation (that is, able to merge two SG segments into a single USB
packet).  But:

	High-speed or slower connections never use a bulk maxpacket
	value larger than 512;

	The SCSI layer does not handle block devices with a block size
	smaller than 512 bytes;

	All the host controllers capable of SuperSpeed operation can
	handle fully general SG;

	Since commit ea44d19 ("usbip: Implement SG support to
	vhci-hcd and stub driver") was merged, the USB/IP driver can
	also handle SG.

Therefore all supported device/controller combinations should be okay
with no need for any special virt_boundary_mask.  So in order to fix
the swiotlb problem, this patch reverts commit 747668d.

Reported-and-tested-by: Piergiorgio Sartor <[email protected]>
Link: https://marc.info/?l=linux-usb&m=157134199501202&w=2
Signed-off-by: Alan Stern <[email protected]>
CC: Seth Bollinger <[email protected]>
CC: <[email protected]>
Fixes: 747668d ("usb-storage: Set virt_boundary_mask to avoid SG overflows")
Acked-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: AlanStern

drivers/usb/storage/scsiglue.c

@@ -68,7 +68,6 @@ static const char* host_info(struct Scsi_Host *host)
 static int slave_alloc (struct scsi_device *sdev)
 {
 	struct us_data *us = host_to_us(sdev->host);
-	int maxp;
 
 	/*
 	 * Set the INQUIRY transfer length to 36.  We don't use any of
@@ -77,15 +76,6 @@ static int slave_alloc (struct scsi_device *sdev)
 	 */
 	sdev->inquiry_len = 36;
 
-	/*
-	 * USB has unusual scatter-gather requirements: the length of each
-	 * scatterlist element except the last must be divisible by the
-	 * Bulk maxpacket value.  Fortunately this value is always a
-	 * power of 2.  Inform the block layer about this requirement.
-	 */
-	maxp = usb_maxpacket(us->pusb_dev, us->recv_bulk_pipe, 0);
-	blk_queue_virt_boundary(sdev->request_queue, maxp - 1);
-
 	/*
 	 * Some host controllers may have alignment requirements.
 	 * We'll play it safe by requiring 512-byte alignment always.