usb/122539: kernel panic: ohci_abort_xfer: not in process context

[John Hein]

The following reply was made to PR usb/122539; it has been noted by GNATS.

From: John Hein <jhein at timing.com>
To: bug-followup at FreeBSD.org, artur.zabronski at gmail.com
Cc: usb at FreeBSD.org
Subject: Re: usb/122539: kernel panic: ohci_abort_xfer: not in process context
Date: Thu, 12 Mar 2009 11:44:21 -0600

 Note: this is not specific to ohci or the device originally used in
 this PR.  The problem is more generic.
 
 This happens for us when hardware flow control is turned on when using
 a usb serial device (specifically an ftdi based one).  Eventually if
 hardware flow has to kick in and RTS is to be set, uftdi_set() is
 called in uftdi.c (old usb stack).
 
 In uftdi_set() there is this...
 
         (void)usbd_do_request(ucom->sc_udev, &req, NULL);
 
 Since we're calling this from the interrupt context, the response
 to the request times out (because the reply is not processed), the
 ohci_abort_xfer which performas the panic because we're not in
 the process context.
 
 Here is a patch that uses the usbd_do_request_async() call (instead of the
 synchronous version) to assert flow control when the input buffer reaches
 the highwater mark (which is detected from within interupt context).
 
 (patch against today's version of uftdi.c in the old usb stack)
 
 Index: sys/legacy/dev/usb/uftdi.c
 ===================================================================
 RCS file: /base/FreeBSD-CVS/src/sys/legacy/dev/usb/uftdi.c,v
 retrieving revision 1.1
 diff -u -p -r1.1 uftdi.c
 --- uftdi.c	23 Feb 2009 18:16:17 -0000	1.1
 +++ uftdi.c	12 Mar 2009 17:34:27 -0000
 @@ -557,7 +557,7 @@ uftdi_set(void *vsc, int portno, int reg
  	DPRINTFN(2,("uftdi_set: reqtype=0x%02x req=0x%02x value=0x%04x "
  		    "index=0x%04x len=%d\n", req.bmRequestType, req.bRequest,
  		    UGETW(req.wValue), UGETW(req.wIndex), UGETW(req.wLength)));
 -	(void)usbd_do_request(ucom->sc_udev, &req, NULL);
 +	(void)usbd_do_request_async(ucom->sc_udev, &req, NULL);
  }
  
  static int
 
 
 This is not specific to FTDI devices.  It would probably be better to
 handle this in the usb serial layer.  Whatever better fix someone
 comes up with should be merged to 7.x if possible (and 6).
 
 I have not yet looked to see if the new usb stack has the same
 problem.  Please let me know if someone does this analysis.