On Tue, Jul 22, 2014 at 12:40:59PM -0400, Peter Hurley wrote: > On 07/22/2014 07:52 AM, xinhui.pan wrote: > > > > 于 2014年07月21日 23:38, Greg KH 写道: > >> On Mon, Jul 21, 2014 at 08:47:16PM +0800, pp wrote: > >>> As reuse the cdev may cause panic. After we unregister the tty device, we > >>> may use tty_hangup() o > >>> other similar function to send a signal(SIGHUP) to process which has > >>> opend our device. But that > >>> not succeed if the process couldn't get the signal. for example, a > >>> process forked > >>> but his parent quited never get SIGHUP. > >>> > >>> Here is our scence. > >>> tty driver register its device and init the cdevs, then process "A" open > >>> one cdev. > >>> tty driver unregister its device and cdev_del the cdevs, call tty_hangup > >>> to (S)send signal SIGHUP to process A. > >>> But that step(S) fails. > >> > >> How can that fail? What driver does this fail for? > > > > hi, Greg > > Thanks for your nice comments. :) > > It's gsm driver that want to unregister/register tty device. We are > > working on our intel mobile phone, > > When the phone goes into airplane-mode, the modem will disconnect from > > system, then gsmld_close() -> gsmld_detach_gsm() -> tty_unregister_device(). > > When the phone leaves airplane-mode, the modem will connect to system, then > > gsmld_open() -> gsmld_attach_gsm() -> tty_register_device() > > In this way how gsm driver works. > > It seems very normal and can work well. :) > > > > But there is always something bad for us to deal with. > > If a process(A, its name) opens the /dev/gsmttyXX, and the process(A) is, > > for example, running with command "A &". > > The process(A) is not able to receive the signal SIGHUP from __tty_hangup() > > -> tty_signal_session_leader(). > > There are several reasons that can stop process(A) from receiving signal > > SIGHUP. > > another example, B is running, and he makes a fork(), A is the child of B, > > then B quit, leave A running. > > in such scenario, A is not able to receive signal SIGHUP, either. > > Anyway, we cannot guarantee process(A) will close /dev/gsmttyXX in time. > > That means we don't know when we can reuse the tty_driver->cdevs[XX]. > > one second, one minute? We don't know. We just don't trust user space. :) > > Or a process could simply ignore SIGHUP, in which case /dev/gsmttyXX > will not be closed until process termination. > > >>> tty driver register its device and (D)init the cdevs again. > >> > >> What driver does this with an "old" device, it should have created a new > >> one, otherwise, as you have pointed out, it's a bug. > >> > > > > I can't agree more with you. we should not use "old" device. > > This is a gsm driver problem. The GSM driver is reusing device indexes > for still-open ttys.
I agree, it should not be doing that at all, please fix that up, and all should be fine. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
