Date: Tue, 10 Sep 2002 15:35:20 -0400 (EDT) From: Robert Watson <rwatson@FreeBSD.ORG> To: Don Lewis <dl-freebsd@catspoiler.org> Cc: bde@zeta.org.au, current@FreeBSD.ORG, jeff@FreeBSD.ORG Subject: Re: vnode lock assertion problem in nfs_link() Message-ID: <Pine.NEB.3.96L.1020910153259.95428D-100000@fledge.watson.org> In-Reply-To: <200209101918.g8AJIHwr095835@gw.catspoiler.org>
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On Tue, 10 Sep 2002, Don Lewis wrote:
> On 11 Sep, Bruce Evans wrote:
> > On Tue, 10 Sep 2002, Don Lewis wrote:
> >
> > I have just one thing to add to Robert's reply.
> >
> >> BTW, is it safe to call ASSERT_VOP_UNLOCKED() in the SMP case after the
> >> reference has been dropped with vput() or vrele()?
> >
> > I think it is. It has some internal locking (v_interlock at least), and
> > only asserts that the vnode is unlocked by curthread so it doesn't matter
> > if another thread locks it.
>
> I'm mostly worried about the vnode being recycled as something else
> after the vput() or vrele() call. I think a better approach would be to
> add the assertion checks to vput() and vrele(), which would mean that we
> could remove most of the checks in the syscall code. The only problems
> we would miss would be when we leak vnode references, but reference
> leaks are a problem anyway. I wish there was a good way to add
> assertion checks for detecting the leaks.
Unfortunately, we can't assert not locked at the end of vput because of
recursive locking of vnodes.
What I would like to see is a check that, when control is returned to
userland, that the thread owns no locks. It's a bit like sleeping while
holding a mutex: don't do that. Also, last time I tried to use the ddb
show lockedvnods command, I got the problem attached below due to locking
issues, which makes it a lot harder to debug locking problems...
Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org Network Associates Laboratories
db> show lockedvnods
Locked vnodes
panic: blockable sleep lock (sleep mutex) mountlist @
../../../kern/vfs_subr.c:2621
Debugger("panic")
Fatal trap 3: breakpoint instruction fault while in kernel mode
instruction pointer = 0x8:0xc0423ed4
stack pointer = 0x10:0xc869b9d0
frame pointer = 0x10:0xc869b9dc
code segment = base 0x0, limit 0xfffff, type 0x1b
= DPL 0, pres 1, def32 1, gran 1
processor eflags = IOPL = 0
current process = 11 (idle)
Stopped at siointr1+0xf4: movl $0,brk_state1.0
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