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UAS: Revert commit 3ae62a4209 ("UAS: fix alignment of scatter/gather segments")

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Commit 3ae62a4209 ("UAS: fix alignment of scatter/gather segments"),
copying a similar commit for usb-storage, 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 the analogous change in usb-storage
interacted badly with commit 09324d32d2 ("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
in the uas driver.  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 ea44d19076 ("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 head
off potential problems similar to those affecting usb-storage, this
patch reverts commit 3ae62a4209.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Oliver Neukum <oneukum@suse.com>
CC: <stable@vger.kernel.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Fixes: 3ae62a4209 ("UAS: fix alignment of scatter/gather segments")
Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910231132470.1878-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alan Stern 2019-10-23 11:34:33 -04:00 committed by Greg Kroah-Hartman
parent 9a97694961
commit 1186f86a71
1 changed files with 0 additions and 20 deletions
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20
drivers/usb/storage/uas.c
View File

@ -789,29 +789,9 @@ static int uas_slave_alloc(struct scsi_device *sdev)
{
struct uas_dev_info *devinfo =
(struct uas_dev_info *)sdev->host->hostdata;
int maxp;
sdev->hostdata = devinfo;
/*
* We have two requirements here. We must satisfy the requirements
* of the physical HC and the demands of the protocol, as we
* definitely want no additional memory allocation in this path
* ruling out using bounce buffers.
*
* For a transmission on USB to continue we must never send
* a package that is smaller than maxpacket. Hence the length of each
* scatterlist element except the last must be divisible by the
* Bulk maxpacket value.
* If the HC does not ensure that through SG,
* the upper layer must do that. We must assume nothing
* about the capabilities off the HC, so we use the most
* pessimistic requirement.
*/
maxp = usb_maxpacket(devinfo->udev, devinfo->data_in_pipe, 0);
blk_queue_virt_boundary(sdev->request_queue, maxp - 1);
/*
* The protocol has no requirements on alignment in the strict sense.
* Controllers may or may not have alignment restrictions.