On Mon, Jun 04, 2012 at 07:04:34PM +0200, Otto Meta wrote: > Hi Johan, > > while working with a USB CDC ACM device I noticed that communication > with the device dies when its TTY is closed while there’s still a lot > of unread data. After reopening the TTY only a few blocks of data are > received and then nothing. This state persists until the device is > disconnected or the kernel module is unloaded. > > This can easily be reproduced if you have a device that sends data which > you can ignore for a while (at least 3968 bytes): > - Have the device send data until usbmon shows no more read URB > submissions > - Close the TTY without reading the data > - Open the TTY and have the device send some data: usbmon shows 16 read > URB submissions at the beginning but once those return, no more > submissions are sent. > > After consulting the source I believe this is caused by a missing > unthrottle in the TTY open/activate function: If the TTY of a CDC ACM > device is closed while it’s throttled, it will stay throttled after > reopening, even though the initial 16 read URB submissions are sent. > > The last working release is 2.6.39.4, the first affected release is 3.0.0 > and all releases since then, including 3.5-rc1, behave the same. > > The problem was probably introduced with this patch: > http://marc.info/?l=linux-usb&m=130104758422681&w=2 > > In acm_tty_open() "acm->throttle = 0;" was removed and no replacement > seems to have been added. The patch below adds throttle-clearing akin to > what happens in acm_tty_unthrottle(). You're absolutely right -- the throttle flags needs to be cleared at open. > The patch was created for 3.5-rc1 but has also been tested successfully > with the stable releases 3.0.32, 3.2.18 and 3.3.7. Yes, this should go into all stable trees >= 3.0. Care to re-submit your patch with a suitable subject line, short description of the problem, and a Signed-of-by-tag? (See Documentation/SubmittingPatches in the kernel source tree for details.) You can add the following tag to your mail to mark that the fix needs to be applied to the stable trees: Cc: <stable@xxxxxxxxxxxxxxx> Please send the patch to Greg KH (CC:ed) while CC:ing the usb mailing list linux-usb@xxxxxxxxxxxxxxx. Thanks for catching this, Johan > Cheers, > Otto > --- linux-3.5-rc1/drivers/usb/class/cdc-acm.c 2012-06-03 03:29:26.000000000 +0200 > +++ linux-3.5-rc1-mod/drivers/usb/class/cdc-acm.c 2012-06-04 16:23:31.038410396 +0200 > @@ -567,6 +567,14 @@ > > usb_autopm_put_interface(acm->control); > > + /* > + * Unthrottle device in case the TTY was closed while throttled. > + */ > + spin_lock_irq(&acm->read_lock); > + acm->throttled = 0; > + acm->throttle_req = 0; > + spin_unlock_irq(&acm->read_lock); > + > if (acm_submit_read_urbs(acm, GFP_KERNEL)) > goto error_submit_read_urbs; > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
