Re: CFR: fifo_open()/fifo_close() patch

Don Lewis wrote:
> On 16 May, Terry Lambert wrote:
> > This is actually pretty bogus.  All VOP's, except those that
> > return (locked) vnodes, or dispose (locked) vnodes that are
> > managed by the FS itself, should have locked vnodes.  There's
> > a nasty race condition that occurs because of the VOP_CLOSE()
> > being called without the vnode locked.
> 
> It does look like v_writecount is somewhat inconsistently locked. The
> comment in <sys/vnode.h> indicates that it should be protected by the
> vnode lock, but some of the INVARIANTS, DIAGNOSTIC, and KASSERT code
> protects it with the vnode interlock, and vn_close() totally fails to
> protect the manipulation of v_writecount.
> 
> I'd toss in calls to vn_lock() and VOP_UNLOCK(), but it looks like while
> most callers of vn_close() call it with the vnode locked, not all do.
> I'm not feeling ambitious enough to track them all down.

You'd have to modify a lot of FS code, as well, to do that,
since they take the lock internal to the VOP_CLOSE code, in
many cases.  Doesn't make it any less broken, though...

-- Terry