On Thu, 13 Jun 2019, Yoshihiro Shimoda wrote:
> This patch fixes an issue that the following error happens on
> swiotlb environment:
>
> xhci-hcd ee000000.usb: swiotlb buffer is full (sz: 524288 bytes), total 32768 (slots), used 1338 (slots)
>
> On the kernel v5.1, block settings of a usb-storage with SuperSpeed
> were the following so that the block layer will allocate buffers
> up to 64 KiB, and then the issue didn't happen.
>
> max_segment_size = 65536
> max_hw_sectors_kb = 1024
>
> After the commit 09324d32d2a0 ("block: force an unlimited segment
> size on queues with a virt boundary") is applied, the block settings
> are the following. So, the block layer will allocate buffers up to
> 1024 KiB, and then the issue happens:
>
> max_segment_size = 4294967295
> max_hw_sectors_kb = 1024
>
> To fix the issue, the usb-storage driver checks the maximum size of
> a mapping for the device and then adjusts the max_hw_sectors_kb
> if required. After this patch is applied, the block settings will
> be the following, and then the issue doesn't happen.
>
> max_segment_size = 4294967295
> max_hw_sectors_kb = 256
>
> Fixes: 09324d32d2a0 ("block: force an unlimited segment size on queues with a virt boundary")
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> ---
> Changes from v1:
> - Call blk_queue_max_hw_sectors() for the maximum size of mapping
> unconditionally to simplify the code by using read the value back
> from the queue in the end.
> - Add a comment on the code.
> - On v1, I got Reviewed-by from Christoph. But, I changed the code a little,
> I removed the Reviewed-by.
>
> drivers/usb/storage/scsiglue.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
> index 59190d8..556bb4f 100644
> --- a/drivers/usb/storage/scsiglue.c
> +++ b/drivers/usb/storage/scsiglue.c
> @@ -28,6 +28,8 @@
> * status of a command.
> */
>
> +#include <linux/blkdev.h>
> +#include <linux/dma-mapping.h>
> #include <linux/module.h>
> #include <linux/mutex.h>
>
> @@ -99,6 +101,7 @@ static int slave_alloc (struct scsi_device *sdev)
> static int slave_configure(struct scsi_device *sdev)
> {
> struct us_data *us = host_to_us(sdev->host);
> + struct device *dev = us->pusb_dev->bus->sysdev;
>
> /*
> * Many devices have trouble transferring more than 32KB at a time,
> @@ -129,6 +132,14 @@ static int slave_configure(struct scsi_device *sdev)
> }
>
> /*
> + * The max_hw_sectors should be up to maximum size of a mapping for
> + * the device. Otherwise, a DMA API might fail on swiotlb environment.
> + */
> + blk_queue_max_hw_sectors(sdev->request_queue,
> + min_t(size_t, queue_max_hw_sectors(sdev->request_queue),
> + dma_max_mapping_size(dev) >> SECTOR_SHIFT));
> +
> + /*
> * Some USB host controllers can't do DMA; they have to use PIO.
> * They indicate this by setting their dma_mask to NULL. For
> * such controllers we need to make sure the block layer sets
Hmmm. Would it be easier instead to copy the DMA mapping parameters
from us->pusb_dev->bus->sysdev into the SCSI host's parent before
calling scsi_add_host()? That way the correct values would be
available from the beginning, so the existing DMA setup would
automatically use the correct sizes.
In fact, the USB core already sets the dma_mask and dma_pfn_offset
fields for the SCSI host's parent (search for dma_mask in
drivers/usb/core/message.c). Is there something else we need to set?
Alan Stern
