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
[EMAIL PROTECTED]      Network Associates Laboratories

db> show lockedvnods
Locked vnodes
panic: blockable sleep lock (sleep mutex) mountlist @

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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