This is a note to let you know that I've just added the patch titled

usb-storage: Revert commit 747668dbc061 ("usb-storage: Set

to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 9a976949613132977098fc49510b46fa8678d864 Mon Sep 17 00:00:00 2001

From: Alan Stern stern@rowland.harvard.edu Date: Mon, 21 Oct 2019 11:48:06 -0400 Subject: usb-storage: Revert commit 747668dbc061 ("usb-storage: Set virt_boundary_mask to avoid SG overflows")

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 piergiorgio.sartor@nexgo.de Link: https://marc.info/?l=linux-usb&m=157134199501202&w=2 Signed-off-by: Alan Stern stern@rowland.harvard.edu CC: Seth Bollinger Seth.Bollinger@digi.com CC: stable@vger.kernel.org Fixes: 747668dbc061 ("usb-storage: Set virt_boundary_mask to avoid SG overflows") Acked-by: Christoph Hellwig hch@lst.de Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910211145520.1673-100000@iolanthe... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/storage/scsiglue.c | 10 ---------- 1 file changed, 10 deletions(-)

diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c index 6737fab94959..54a3c8195c96 100644 --- a/drivers/usb/storage/scsiglue.c +++ b/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.