Messages in this thread | | | Date | Wed, 23 Jul 2014 12:04:21 -0400 | From | Peter Hurley <> | Subject | Re: [PATCH] tty/tty_io.c: make a check before reuse cdev |
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Hi Xinhui,
On 07/23/2014 05:21 AM, xinhui.pan wrote: > 于 2014年07月23日 00:40, Peter Hurley 写道: >> 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:
>>>>> 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. >> >> The GSM driver uses a global table, gsm_mux[], to allocate device indexes >> but prematurely clears the table entry in gsm_mux_cleanup(). If instead, >> clearing the gsm_mux table entry were deferred to gsm_mux_free(), then >> device indexes would not be getting reused until after the last tty >> associated with the last gsm attach was closed. >> > > Very nice solution. We will check if this can cause any risk, both to kernel and user space. > Using a new tty base to register with new cdevs may give us more chance to wait PROCESS quit/close. > when total 256 tty used up, what we should do is still in discuss.
I saw your patch for the use of gsm->num before gsm_activate_mux() has allocated the table entry; thanks for fixing that.
As for what to do if all the gsm_mux table entries are used: if the error is infrequent, I suggest simply returning an error which is what the driver does currently. Otherwise, a more dynamic allocation scheme may be required.
I did notice while reviewing the error handling that gsmld_open() will leak the entire composite ldisc data allocated by gsm_alloc_mux() if gsmld_attach_gsm() fails.
Regards, Peter Hurley
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