VOP_LOCK() may be handed a vnode that is concurrently reclaimed.
unionfs_lock() accounts for this by checking for empty vnode private
data under the interlock. But it incorrectly asserts that the vnode
is using the unionfs dispatch table before making this check.
Reverse the order, and also update KASSERT_UNIONFS_VNODE() to provide
more useful information.
Reported by: pho
unionfs: allow lock recursion when reclaiming the root vnode
The unionfs root vnode will always share a lock with its lower vnode.
If unionfs was mounted with the 'below' option, this will also be the
vnode covered by the unionfs mount. During unmount, the covered vnode
will be locked by dounmount() while the unionfs root vnode will be
locked by vgone(). This effectively requires recursion on the same
underlying like, albeit through two different vnodes.
Reported by: pho
unionfs: do not force LK_NOWAIT if VI_OWEINACT is set
I see no apparent need to avoid waiting on the lock just because
vinactive() may be called on another thread while the thread that
cleared the vnode refcount has the lock dropped. In fact, this
can at least lead to a panic of the form "vn_lock: error <errno>
incompatible with flags" if LK_RETRY was passed to VOP_LOCK().
In this case LK_NOWAIT may cause the underlying FS to return an
error which is incompatible with LK_RETRY.
Reported by: pho