FreeBSD 11.0-ALPHA5 r302256 kernel panic in filt_proc()

[Konstantin Belousov]

On Wed, Jun 29, 2016 at 02:44:08PM -0700, Don Lewis wrote:
> #10 0xffffffff80a02ddc in filt_proc (kn=0xfffff803c5679a80, 
>     hint=<value optimized out>) at /usr/src/sys/kern/kern_event.c:473
> #11 0xffffffff80a0173b in knote (list=<value optimized out>, hint=2147483648, 
>     lockflags=<value optimized out>) at /usr/src/sys/kern/kern_event.c:2045
> #12 0xffffffff80a0710e in exit1 (td=<value optimized out>, 
>     rval=<value optimized out>, signo=<value optimized out>)
>     at /usr/src/sys/kern/kern_exit.c:515
> #13 0xffffffff80a0677d in sys_sys_exit (td=0xfffff803c5679a80, 
>     uap=<value optimized out>) at /usr/src/sys/kern/kern_exit.c:178
> #14 0xffffffff80eb8b2b in amd64_syscall (td=0xfffff80096b49500, traced=0)
>     at subr_syscall.c:135
> #15 0xffffffff80e98d9b in Xfast_syscall ()
>     at /usr/src/sys/amd64/amd64/exception.S:396
> #16 0x00000008009298ca in ?? ()
> Previous frame inner to this frame (corrupt stack?)
> Current language:  auto; currently minimal
> (kgdb) 
> 
> 
> The line numbers above seem to be off.  With kgdb from ports I see:
> 
> (kgdb) up
> #12 filt_proc (kn=0xfffff803c5679a80, hint=<optimized out>)
>     at /usr/src/sys/kern/kern_event.c:466
> 466				kn->kn_data = KW_EXITCODE(p->p_xexit, p->p_xsig);
> (kgdb) print kn
> $1 = (struct knote *) 0xfffff803c5679a80
> (kgdb) print p
> $2 = (struct proc *) 0x0
> 
Please print out the knote, do 'p *kn'.  I am esp. interested in the
kn->kn_status value.  It seems that the knote was already detached,