[lkml]   [2013]   [Mar]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v3 00/23] ldisc fixes
On 03/05/2013 11:20 PM, Peter Hurley wrote:
> [--cc Alan Cox]
> On Tue, 2013-03-05 at 21:50 +0100, Sebastian Andrzej Siewior wrote:
>> * Peter Hurley | 2013-02-05 15:20:15 [-0500]:
>>> Please re-test with your dummy_hcd/g_nokia testcase, although
>>> I'm not convinced that usb gadget is using tty_hangup() appropriately.
>>> tty drivers use this for async carrier loss coming from an IRQ
>>> which will be disabled if the tty has been shutdown. Does gserial
>>> prevent async hangup to a dead tty in a similar fashion?
>> Not sure I understood. tty_hangup() is only called from within
>> gserial_disconnect() which calls right after usb_ep_disable(). After
>> usb_ep_disable() no further serial packets can be received until the
>> endpoints are re-enabled. This happens in gserial_connect().
> That's why I asked. There are two potential issues:
> First, tty_hangup() is asynchronous -- ie., it returns immediately. It
> does not wait for the tty device to actually perform the hangup. So if
> the gadget layers start cleanup immediately after, expecting that they
> won't get a flurry of tty calls, that would be bad.

Sorry, I missed what driver is this?

> tty_vhangup() is synchronous -- ie., you wait while it cleans up. This
> is what the usb serial core does on it's disconnect() method. But I
> didn't research further if the circumstances were the same.

Even when tty_vhangup returns, it does not guarantee a closed tty. And
it also does not guarantee that any of tty->ops won't be called. The
latter is true only for devices that can be consoles. (For those,
file->ops are not redirected.) In that case one needs to wait for
port->count to become 0.

suse labs

 \ /
  Last update: 2013-03-06 00:21    [W:3.627 / U:0.228 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site