Date: Tue, 9 Jun 2009 09:45:49 -0700 From: "Matthew Fleming" <matthew.fleming@isilon.com> To: "Kostik Belousov" <kostikbel@gmail.com>, "John Baldwin" <jhb@freebsd.org> Cc: Yuri Pankov <yuri.pankov@gmail.com>, freebsd-current@freebsd.org, Paul Saab <ps@freebsd.org> Subject: RE: panic: knlist not locked, but should be Message-ID: <06D5F9F6F655AD4C92E28B662F7F853E02CC8A29@seaxch09.desktop.isilon.com> In-Reply-To: <20090609163005.GD75569@deviant.kiev.zoral.com.ua> References: <20090609110540.GA1290@darklight.homeunix.org><200906090937.37562.jhb@freebsd.org><20090609135145.GB1290@darklight.homeunix.org><200906091059.15278.jhb@freebsd.org> <20090609163005.GD75569@deviant.kiev.zoral.com.ua>
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> This appears to be an interaction with the recent changes to use=20
> shared vnode locks for writes on ZFS. Hmm, I think it may be ok to=20
> use a shared vnode lock for kevents on vnodes though. The vnode=20
> interlock should be sufficient locking for what little work the kevent
> filters do. As a quick hack for now the MNT_SHARED_WRITES() stuff=20
> could avoid using shared locks 'if (!VN_KNLIST_EMPTY(vp))', but I=20
> think the longer term fix is to not use the vnode locks for vnode
kevents, but use the interlock instead.
I tried (briefly) using the interlock since Isilon's vnode lock is
cluster wide (in our 6.1 based code we got away with using Giant). This
got me a LOR report on the interlock:
/*
* kqueue/VFS interaction
*/
{ "kqueue", &lock_class_mtx_sleep },
{ "struct mount mtx", &lock_class_mtx_sleep },
{ "vnode interlock", &lock_class_mtx_sleep },
{ NULL, NULL },
since knote() will take first the list->kl_lock and then the kqueue
lock. I didn't spend any time on it, and switched to using the vnode
v_lock for my purposes. But someone added that lock ordering (r166421)
for a reason.
Cheers,
matthew
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