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From: Matthew Jacob <mjacob@feral.com>
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To: Andrew Gallatin <gallatin@cs.duke.edu>
Cc: freebsd-alpha@FreeBSD.ORG
Subject: Re: user process faulting on kernel address
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Hah. On a related note, the faulting address for dumps that SIGSEGV' is in
fact, CURSIG in the kernel. Same ra range- user stack address.

D'ya think they're related? Doug? 

> 
> When running a linuxthreads app which basically sits in a loop
> doing a pthread_create()/pthread_join() of a thread which just
> exits, I'll occasionally see a very interesting thing -- 
> the app dies on an instruction fault on a kernel address.
> 
> Enabling the DEBUG printtrap() calls in trap yeilds this information:
> 
> login: 
> fatal user trap:
> 
>     trap entry = 0x2 (memory management fault)
>     a0         = 0xfffffc0000418be0
>     a1         = 0x1
>     a2         = 0xffffffffffffffff
>     pc         = 0xfffffc0000418be0
>     ra         = 0x11ffbfc4
>     curproc    = 0xfffffe0006824cc0
>         pid = 18788, comm = ex6
> 
> 
> Note that it is an instruction fault (a2 == -1) and the faulting
> address maps to the bottom of witness_exit:
> 
> (kgdb) l *0xfffffc0000418be0
> 0xfffffc0000418be0 is in witness_exit (../../kern/kern_mutex.c:1262).
> 1257            m->mtx_line = line;
> 1258            m->mtx_file = file;
> 1259            p = curproc;
> 1260            MPASS(m->mtx_held.le_prev == NULL);
> 1261            LIST_INSERT_HEAD(&p->p_heldmtx, (struct mtx*)m, mtx_held);
> 1262    }
> 1263
> 1264    void
> 1265    witness_exit(struct mtx *m, int flags, const char *file, int line)
> 1266    {
> 
> 
> The $ra looks reasonable, it is at least a userspace stack address.
> 
> I think somebody saw this a while ago, but I cannot find their
> message..
> 
> Any ideas?
> 
> Drew
> 
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