Re: tty TTY_HUPPED anomaly
From: Mark Hounschell
Date: Fri Dec 23 2011 - 13:47:07 EST
On 12/23/2011 09:51 AM, Mark Hounschell wrote:
I have an application that has seemingly been stable for many years and
even using the 3.1.1 kernel all is fine. I'm using the openSuSE
distribution. All is good with the openSuSE-11.4 dist and the 3.1.1
kernel. We recently started testing this application on openSuSE-12.1
using the same vanilla 3.1.1 kernel and now we have problems with just
about all out tty/serial related devices that we use. I thought the
problem maybe an openSuSE glibc problem so I built and ran the
openSuSE-12.1 version of glibc on the openSuSE-11.4 dist but the
application worked just fine. So I started looking at the kernel and one
of our serial devices that fails. I choose the Synclink GT because its
driver is "in kernel".
In our application with this particular card, the following TIOCSETD
ioctl is this code snippet fails most of the time.
int32_t hdlc_disc = N_HDLC;
Q->fd = open(Q->FileName, (O_RDWR | O_NONBLOCK), 0);
if (Q->fd < 0)
return (FALSE);
Q->File = fdopen(Q->fd, "rw");
fcntl(Q->fd, F_SETFL, fcntl(S->fd,F_GETFL) & ~O_NONBLOCK);
if (ioctl(Q->fd, TIOCSETD, &hdlc_disc) < 0) {
perror("SCM_open_port: TIOCSETD failed: ");
return (FALSE);
}
The kernel code that results in the above code snippet failure is the
following section of the tty_set_ldisc function in tty_io.c.
if (test_bit(TTY_HUPPED, &tty->flags)) {
/* We were raced by the hangup method. It will have stomped
the ldisc data and closed the ldisc down */
clear_bit(TTY_LDISC_CHANGING, &tty->flags);
mutex_unlock(&tty->ldisc_mutex);
tty_ldisc_put(new_ldisc);
tty_unlock();
return -EIO;
}
I do not really understand what TTY_HUPPED is or how it could be getting
set. I look at it when the tty_set_ldisc function is entered and it is
not set. Some where between entrance of the tty_set_ldisc and getting to
the above code TTY_HUPPED gets set causing the -EIO return.
I see nothing in my code that should cause this to happen. At start up
time a thread for each port used does this then goes to sleep. Again, I
can't understand why now with openSuSE-12.1 this starts happening. Can
someone help me understand why this might happen. I don't know if it is
me, the dist, or the kernel. Frequently it all works at startup and will
eventually fail during operation.
Other serial cards that I also have similar problems with (different
ioctls) are various Digi serial cards. I haven't look into the kernel to
see what is happening with those as yet but am sure the problem is
related. Sometimes they work, most of the time they do not.
More info:
I turned the TTY_DEBUG_HANGUP and added some additional printks. You see
below the first port works just fine but the second fails because
something is calling the tty_hangup function around 70usecs after I open
the device???
What and Why???
Dec 23 13:36:19 harley kernel: [ 1139.456286] tty_open: opening ttySLG0...
Dec 23 13:36:19 harley kernel: [ 1139.456357] tiocsetd: Entered. tty =
0xe6b60c00 p = 0x0000000d tty->flags = 0x00000a00
Dec 23 13:36:19 harley kernel: [ 1139.456359] tiocsetd: setting tty
ldisc to 0x0000000d
Dec 23 13:36:19 harley kernel: [ 1139.456361] tty_set_ldisc: Entered.
tty = 0xe6b60c00 ldisk = 0x0000000d tty->flags = 0x00000a00 TTY_HUPPED =
0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456363] tty_set_ldisc:
TTY_HUPPED-a = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456364] tty_set_ldisc:
TTY_HUPPED-b = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456365] tty_set_ldisc:
TTY_HUPPED-0 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456368] tty_set_ldisc:
TTY_HUPPED-1 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456369] tty_set_ldisc:
TTY_HUPPED-2 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456370] tty_set_ldisc:
TTY_HUPPED-3 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456373] tty_set_ldisc: retval from
tty_ldisc_wait_idle = 0x00000000 TTY_HUPPED = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456384] tty_set_ldisc: returning
0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.456385] tiocsetd: Complete. ret =
0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458194] tty_open: opening ttySLG1...
Dec 23 13:36:19 harley kernel: [ 1139.458270] tty_hangup: ttySLG1 hangup...
Dec 23 13:36:19 harley kernel: [ 1139.458274] tiocsetd: Entered. tty =
0xe6b60800 p = 0x0000000d tty->flags = 0x00000a00
Dec 23 13:36:19 harley kernel: [ 1139.458276] tiocsetd: setting tty
ldisc to 0x0000000d
Dec 23 13:36:19 harley kernel: [ 1139.458278] tty_set_ldisc: Entered.
tty = 0xe6b60800 ldisk = 0x0000000d tty->flags = 0x00000a00 TTY_HUPPED =
0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458281] tty_set_ldisc:
TTY_HUPPED-a = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458283] tty_set_ldisc:
TTY_HUPPED-b = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458284] tty_set_ldisc:
TTY_HUPPED-0 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458288] tty_set_ldisc:
TTY_HUPPED-1 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458289] tty_set_ldisc:
TTY_HUPPED-2 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458290] tty_set_ldisc:
TTY_HUPPED-3 = 0x00000000
Dec 23 13:36:19 harley kernel: [ 1139.458307] tty_hangup: ttySLG1 hangup...
Dec 23 13:36:19 harley kernel: [ 1139.458309] __tty_hangup: Entered for
tty = 0xe6b60800
Dec 23 13:36:19 harley kernel: [ 1139.458340] __tty_hangup: Setting
TTY_HUPPED for tty at 0xe6b60800
Dec 23 13:36:19 harley kernel: [ 1139.458347] tty_set_ldisc: retval from
tty_ldisc_wait_idle = 0x00000000 TTY_HUPPED = 0x00040000
Dec 23 13:36:19 harley kernel: [ 1139.458349] tty_set_ldisc: tty->flags
= 0x00040a02 TTY_HUPPED = 0x00040000 returning -EIO
Dec 23 13:36:19 harley kernel: [ 1139.458350] tiocsetd: Complete. ret =
0xfffffffb
Thanks again for any help on this
Regards
Mark
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