10.1 regression: process using serial port becomes unkillable when no modem control signals

[Konstantin Belousov]

On Fri, Dec 05, 2014 at 06:44:51PM +1100, Jan Mikkelsen wrote:
> Hi,
> 
> I have just found this problem on a machine upgraded to 10.1.
> 
> When running mgetty on a serial port with nothing connected and then killing it the process becomes unkillable. This prevents ???shutdown -r??? from completing, which is particularly annoying.
> 
> Giving the serial port a device which provides the right modem control signals lets the process exit immediately. The same hardware with 9.3 was fine.
> 
> Below is the kernel stack trace on the unkillable process.
> 
> Does this ring any bells for anyone?

This sounds as something that might be fixed by r272786 and r272789
in HEAD.  I did not looked into details too close.

The changes are not in stable/10, apply manually and test.

> 
> Thanks,
> 
> Jan Mikkelsen
> 
> (kgdb) bt
> #0  sched_switch (td=0xfffff80236e1a920, newtd=<value optimized out>, flags=<value optimized out>) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/sched_ule.c:1945
> #1  0xffffffff80939ba1 in mi_switch (flags=260, newtd=0x0) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/kern_synch.c:494
> #2  0xffffffff80976d6b in sleepq_catch_signals (wchan=0xfffff8000c7344b8, pri=0) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/subr_sleepqueue.c:426
> #3  0xffffffff80976c1f in sleepq_wait_sig (wchan=0x0, pri=0) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/subr_sleepqueue.c:631
> #4  0xffffffff808e345a in _cv_wait_sig (cvp=0xfffff8000c7344b8, lock=0xfffff8000c734408) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/kern_condvar.c:258
> #5  0xffffffff809957a5 in ttydev_leave (tp=0xfffff8000c734400) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/tty.c:1392
> #6  0xffffffff80994d30 in ttydev_close (dev=<value optimized out>, fflag=0, devtype=0, td=0x0) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/tty.c:353
> #7  0xffffffff8081ec63 in devfs_close (ap=0xfffffe0c541d57e0) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/fs/devfs/devfs_vnops.c:592
> #8  0xffffffff80e6d281 in VOP_CLOSE_APV (vop=<value optimized out>, a=<value optimized out>) at vnode_if.c:535
> #9  0xffffffff809df673 in vn_close (vp=0xfffff80236a6f588, flags=3, file_cred=0xfffff806a300b200, td=0xfffff80236e1a920) at vnode_if.h:225
> #10 0xffffffff809de4c8 in vn_closefile (fp=0xfffff8001243d9b0, td=0xfffff80236e1a920) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/vfs_vnops.c:1557
> #11 0xffffffff808204bc in devfs_close_f (fp=0xfffff8001243d9b0, td=0x0) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/fs/devfs/devfs_vnops.c:611
> #12 0xffffffff808ed249 in _fdrop (fp=0xfffff8001243d9b0, td=0x0) at file.h:343
> #13 0xffffffff808ef9ae in closef (fp=<value optimized out>, td=<value optimized out>) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/kern_descrip.c:2335
> #14 0xffffffff808ef5c9 in fdescfree (td=0xfffff80236e1a920) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/kern_descrip.c:2103
> #15 0xffffffff808fb8fb in exit1 (td=0xfffff80236e1a920, rv=<value optimized out>) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/kern_exit.c:329
> #16 0xffffffff808fb37e in sys_sys_exit (td=0x0, uap=<value optimized out>) at /usr/home/janm/p4/freebsd-image-std-2014.2/FreeBSD/src/sys/kern/kern_exit.c:153
> #17 0xffffffff80d4f521 in amd64_syscall (td=0xfffff80236e1a920, traced=0) at subr_syscall.c:134
> 
> 
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