[PATCH v3] usb-storage: Add a limitation for blk_queue_max_hw_sectors()

[PATCH v3] usb-storage: Add a limitation for blk_queue_max_hw_sectors()

[Yoshihiro Shimoda]

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@renesas.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
---
 This patch can be applied on v5.3-rc1.

 Changes from v2:
 - Add Alan's Acked-by.
 https://patchwork.kernel.org/patch/10992539/

 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.
 https://patchwork.kernel.org/patch/10992985/

 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 3079024..05b8021 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
-- 
2.7.4

Re: [PATCH v3] usb-storage: Add a limitation for blk_queue_max_hw_sectors()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>