Re: [PATCH 3.12 033/118] usb: xhci: Link TRB must not occur withina USB payload burst

From: walt
Date: Fri Jan 03 2014 - 10:40:44 EST

On 01/02/2014 11:15 AM, Sarah Sharp wrote:
> On Tue, Dec 31, 2013 at 12:40:16PM -0800, walt wrote:
>> On 12/18/2013 01:11 PM, Greg Kroah-Hartman wrote:
>>> 3.12-stable review patch. If anyone has any objections, please let me know.
>>> ------------------
>>> From: David Laight <David.Laight@xxxxxxxxxx>
>>> commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e upstream.
>>> Section of rev 1.0 of the xhci specification states that a link TRB
>>> can only occur at a boundary between underlying USB frames (512 bytes for
>>> high speed devices).
>>> If this isn't done the USB frames aren't formatted correctly and, for example,
>>> the USB3 ethernet ax88179_178a card will stop sending...
>> Unfortunately this patch causes a regression when copying large files to my
>> outboard USB3 drive. (Nothing at all to do with networking.)

> Do you have CONFIG_USB_DEBUG turned on for 3.13? If so, you should see
> dmesg output from this statement shortly before your drive fails:
> if (num_trbs >= TRBS_PER_SEGMENT) {
> xhci_err(xhci, "Too many fragments %d, max %d\n",
> num_trbs, TRBS_PER_SEGMENT - 1);
> return -ENOMEM;
> }

Well, the answers depend on whether the usb3 drive uses logical volumes or not
(lvm2), which I can't explain. What I've described so far is with lvm2.

When using lvm2 on the usb3 drive, turning on USB_DEBUG has *no* effect -- the
console prints two or three lines stating that the ext4 journal has quit and
the drive is remounted ro. That particular drive stays wedged until the next
reboot, but no other ill effects to the system.

OTOH, when I put a disk with just an ordinary ext4 partition in the usb3 dock,
(no logical volumes) the copy failure becomes catastrophic, with kernel panic
messages, leaving the system unresponsive and needing a hard reset to recover.

I also tried your other suggestion:

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 4265b48..1a6a43d 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -4714,7 +4714,7 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
int retval;

/* Accept arbitrarily long scatter-gather lists */
- hcd->self.sg_tablesize = ~0;
+ hcd->self.sg_tablesize = 31;

/* support to build packet from discontinuous buffers */
hcd->self.no_sg_constraint = 1;

Sadly it didn't fix the problem. Did I get the patch right?

Thanks for your help, and I'm happy to try more ideas, as always.

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