Date: Sun, 2 Mar 2008 11:53:34 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Kostik Belousov <kostikbel@gmail.com> Cc: current@freebsd.org Subject: Re: knlsit_cleardel() panic Message-ID: <20080302195334.GI96595@funkthat.com> In-Reply-To: <20080302152523.GO57756@deviant.kiev.zoral.com.ua> References: <20080302152523.GO57756@deviant.kiev.zoral.com.ua>
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Kostik Belousov wrote this message on Sun, Mar 02, 2008 at 17:25 +0200:
> The panic below was already reported, but now I got it on my desktop
> and was able to investigate further.
>
> #5 0xc06daf36 in trap (frame=0xe8093b1c)
> at /usr/bsd/src/sys/i386/i386/trap.c:490
> #6 0xc06c0b4b in calltrap () at /usr/bsd/src/sys/i386/i386/exception.s:139
> #7 0xc0493968 in knlist_cleardel (knl=0xcabec128, td=0x0, islocked=1,
> killkn=0) at atomic.h:149
> #8 0xc04f520c in pipeclose (cpipe=0xcabec0b8)
> at /usr/bsd/src/sys/kern/sys_pipe.c:1508
> #9 0xc04f5320 in pipe_close (fp=0xc5ce8630, td=0xcac01aa0)
> at /usr/bsd/src/sys/kern/sys_pipe.c:1425
> #10 0xc0489442 in fdrop (fp=0xc5ce8630, td=0xcac01aa0) at file.h:297
> #11 0xc048accf in closef (fp=0xc5ce8630, td=0xcac01aa0)
> at /usr/bsd/src/sys/kern/kern_descrip.c:1958
> #12 0xc048b1ff in kern_close (td=0xcac01aa0, fd=10)
> at /usr/bsd/src/sys/kern/kern_descrip.c:1054
> #13 0xc048b2da in close (td=0xcac01aa0, uap=0xe8093cfc)
> at /usr/bsd/src/sys/kern/kern_descrip.c:1006
> ---Type <return> to continue, or q <return> to quit---
> #14 0xc06da865 in syscall (frame=0xe8093d38)
> at /usr/bsd/src/sys/i386/i386/trap.c:1035
> #15 0xc06c0bb0 in Xint0x80_syscall ()
> at /usr/bsd/src/sys/i386/i386/exception.s:196
>
> At the frame 8, we have
> (kgdb) p/x *(knl->kl_list->slh_first)
> $9 = {kn_link = {sle_next = 0x0}, kn_selnext = {sle_next = 0x0},
> kn_knlist = 0x0, kn_tqe = {tqe_next = 0xc58de484, tqe_prev = 0xc5e9ab20},
> kn_kq = 0x0, kn_kevent = {ident = 0x0, filter = 0x0, flags = 0x0,
> fflags = 0x0, data = 0x0, udata = 0x0}, kn_status = 0x20,
> kn_sfflags = 0x0, kn_sdata = 0x0, kn_ptr = {p_fp = 0x0, p_proc = 0x0,
> p_aio = 0x0, p_lio = 0x0}, kn_fop = 0x0, kn_hook = 0x0}
>
> The knote is KN_MARKER, and the kn_kq is NULL. The result is that KQ_LOCK
> in the knlist_cleardel()::SLIST_FOREACH_SAFE() loop dereferences NULL and
> panics.
>
> Does the following change makes any sense?
I thought this was a bug, but upon further examination, there is
something wrong... a KN_MARKER knote should never be on the knlist..
It is only ever added to kq's even list, never to an object's list...
If you could walk the knl->kl_list through kn_selnext, and ensure
that the kn w/ kN_MARKER exists would be good... It should be the
last one as kn_selnext is NULL...
I can't think of a way that this can happen, as the only way to get
on the knlist is by calling knlist_add, and it should only ever be
called from f_attach, which is called in one place, and has to have
kn_kq set properly... Are there any custom patches on the system?
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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