Commit 747668dbc061 ("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
09324d32d2a0 ("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 ea44d190764b ("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 747668dbc061.

Reported-and-tested-by: Piergiorgio Sartor <>
Signed-off-by: Alan Stern <>
CC: Seth Bollinger <>
CC: <>



 drivers/usb/storage/scsiglue.c |   10 ----------
 1 file changed, 10 deletions(-)

Index: usb-devel/drivers/usb/storage/scsiglue.c
--- usb-devel.orig/drivers/usb/storage/scsiglue.c
+++ usb-devel/drivers/usb/storage/scsiglue.c
@@ -68,7 +68,6 @@ static const char* host_info(struct Scsi
 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
@@ -78,15 +77,6 @@ static int slave_alloc (struct scsi_devi
        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.

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