Date: Mon, 03 Jul 2006 16:20:28 +0200 From: Fredrik Lindberg <fli+freebsd-current@shapeshifter.se> To: freebsd-current@freebsd.org Subject: panic: knlist locked, but should not be Message-ID: <44A927AC.7080807@shapeshifter.se>
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Hi,
I'm hitting this "knlist locked"-panic when using BPF descriptors
together with kqueue/kevent.
panic: knlist locked, but should not be
#10 0xc051a1e3 in knlist_add (knl=0xc3b69460, kn=0xc3ad65d8, islocked=0)
at /usr/src/sys/kern/kern_event.c:1571
#11 0xc059c5de in bpfkqfilter (dev=0x12, kn=0xc3ad65d8) at
/usr/src/sys/net/bpf.c:1194
#12 0xc050d9e6 in giant_kqfilter (dev=0xc38f9d00, kn=0xc3ad65d8)
at /usr/src/sys/kern/kern_conf.c:336
#13 0xc04e9580 in devfs_kqfilter_f (fp=0xc3ad40d8, kn=0xc3ad65d8)
at /usr/src/sys/fs/devfs/devfs_vnops.c:444
#14 0xc0517e6d in filt_fileattach (kn=0x12) at file.h:305
#15 0xc0518eb0 in kqueue_register (kq=0xc3923780, kev=0xe3a67b9c,
td=0xc3714a20, waitok=1)
at /usr/src/sys/kern/kern_event.c:902
#16 0xc05185f4 in kern_kevent (td=0xc3714a20, fd=3, nchanges=1,
nevents=0, k_ops=0xe3a67c70,
timeout=0x0) at /usr/src/sys/kern/kern_event.c:640
#17 0xc0518491 in kevent (td=0xc3714a20, uap=0xe3a67d04) at
/usr/src/sys/kern/kern_event.c:572
I thinks the problem is as follows, islocked is 0 which triggers
the macro KNL_ASSERT_LOCK(knl, islocked);
(It will only bite you if you run with INVARIANTS on)
The knlist is initialized with the same mutex that protects the
rest of the bpf_d structure.
bpfopen(), sys/net/bpf.c:383
knlist_init(&d->bd_sel.si_note, &d->bd_mtx, NULL, NULL, NULL);
In bpfkqfilter() and filt_bpfdetach() this mutex is acquired with
BPFD_LOCK() before calling knlist_add()/knlist_remove()
#define BPFD_LOCK(bd) mtx_lock(&(bd)->bd_mtx)
Hence, the knlist lock IS locked despite being called with islocked = 0.
If using the same mutex doesn't cause any additional problems,
(I haven't noticed anything yet, but there could of course be issues
that I've overlooked), I think knlist_add should be called
with islocked = 1. A suggested patch is attached.
Fredrik Lindberg
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name="bpf.c-knlist-20060703.patch"
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filename="bpf.c-knlist-20060703.patch"
Index: bpf.c
===================================================================
RCS file: /home/ncvs/src/sys/net/bpf.c,v
retrieving revision 1.168
diff -u -r1.168 bpf.c
--- bpf.c 15 Jun 2006 15:39:12 -0000 1.168
+++ bpf.c 3 Jul 2006 11:36:30 -0000
@@ -1152,7 +1152,7 @@
d->bd_pid = curthread->td_proc->p_pid;
kn->kn_fop = &bpfread_filtops;
kn->kn_hook = d;
- knlist_add(&d->bd_sel.si_note, kn, 0);
+ knlist_add(&d->bd_sel.si_note, kn, 1);
BPFD_UNLOCK(d);
return (0);
@@ -1164,7 +1164,7 @@
struct bpf_d *d = (struct bpf_d *)kn->kn_hook;
BPFD_LOCK(d);
- knlist_remove(&d->bd_sel.si_note, kn, 0);
+ knlist_remove(&d->bd_sel.si_note, kn, 1);
BPFD_UNLOCK(d);
}
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