alq_open_flags() panics in _mtx_lock_flags()

Lawrence Stewart lstewart at
Mon Oct 3 00:58:33 UTC 2011

[trimmed current@ from CC]

Hi Lev,

On 10/03/11 02:32, Lev Serebryakov wrote:
> Hello, FreeBSD.
>   I'm trying to create logging queue with alq kernel API. I call
>   alq_open_flags() like this in my module:
> error = alq_open_flags(&sc->sc_alq, sc->sc_vnode_name,
>      curthread->td_ucred, ALQ_DEFAULT_CMODE,
>      sizeof(struct g_log_entry), ALQ_ORDERED);
>   and my system (10-CURRENT) panics with this stack trace (top frames
>   are DDB-related, so I omit them):
> #5  0xc06101c3 in kdb_trap (type=12, code=0, tf=0xc4e29990)
>      at /usr/home/lev/FreeBSD-head/sys/kern/subr_kdb.c:620
> #6  0xc08290af in trap_fatal (frame=0xc4e29990, eva=136)
>      at /usr/home/lev/FreeBSD-head/sys/i386/i386/trap.c:958
> #7  0xc08292c0 in trap_pfault (frame=0xc4e29990, usermode=0, eva=136)
>      at /usr/home/lev/FreeBSD-head/sys/i386/i386/trap.c:880
> #8  0xc0829f46 in trap (frame=0xc4e29990)
>      at /usr/home/lev/FreeBSD-head/sys/i386/i386/trap.c:555
> #9  0xc0812e7c in calltrap ()
>      at /usr/home/lev/FreeBSD-head/sys/i386/i386/exception.s:168
> #10 0xc05cafc0 in _mtx_lock_flags (m=0x78, opts=0,
>      file=0xc088c140 "/usr/home/lev/FreeBSD-head/sys/kern/vfs_subr.c",
>      line=2169) at /usr/home/lev/FreeBSD-head/sys/kern/kern_mutex.c:194
> #11 0xc0672eb2 in vref (vp=0x0)
>      at /usr/home/lev/FreeBSD-head/sys/kern/vfs_subr.c:2169
> #12 0xc066932f in namei (ndp=0xc4e29b74)
>      at /usr/home/lev/FreeBSD-head/sys/kern/vfs_lookup.c:264
> #13 0xc0682900 in vn_open_cred (ndp=0xc4e29b74, flagp=0xc4e29be8, cmode=384,
>      vn_open_flags=0, cred=0xc50fee80, fp=0x0)
>      at /usr/home/lev/FreeBSD-head/sys/kern/vfs_vnops.c:137
> #14 0xc5c42609 in alq_open_flags (alqp=0xc550dc08,
>      file=0xc5108d40 "/usr/ada4.log", cred=0xc50fee80, cmode=384, size=28,
>      flags=16)
>      at /usr/home/lev/FreeBSD-head/sys/modules/alq/../../kern/kern_alq.c:451
>    It seems, that vref() get NULL instead of valid pointer to struct
>   vnode. But I have no idea -- why?! Yes, I have no such file created,
>   but man alq(9) says, that it will create file for me. And if I point
>   to existed file, it panic anyway.
>    What do I do wrong?!

I don't see anything obviously wrong with your call to alq_open_flags(), 
other than that I think you want to set your buffer size to be a 
multiple of "sizeof(struct g_log_entry)". The small queue size wouldn't 
cause the panic you're seeing though.

It's hard to draw any real conclusions without seeing your code. Are you 
able to share it?


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