I tried booting a kernel with lock checking enabled and got the
following panic:
panic: mutex vnode interlock owned at vnode_if.h:24
panic()
_mtx_assert()
VOP_ISLOCKED()
vop_unlock_pre()
vput()
kern_mkdir()+0x9e - the first call to vput() to handle the "found" case?
start_init()
fork_exit()
fork_trampoline()
I believe there is a logic error in the VOP_UNLOCK() assertion logic.
In vput(), there is the following code:
VI_LOCK(vp);
/* Skip this v_writecount check if we're going to panic below. */
KASSERT(vp->v_writecount < vp->v_usecount || vp->v_usecount < 1,
("vput: missed vn_close"));
if (vp->v_usecount > 1) {
vp->v_usecount--;
VOP_UNLOCK(vp, LK_INTERLOCK, td);
return;
}
which looks reasonable. VOP_UNLOCK() starts off with the following
code:
struct vop_unlock_args a;
int rc;
a.a_desc = VDESC(vop_unlock);
a.a_vp = vp;
a.a_flags = flags;
a.a_td = td;
#ifdef DEBUG_VFS_LOCKS
vop_unlock_pre(&a);
#endif
Then vop_unlock_pre() contains the following code:
if (a->a_flags & LK_INTERLOCK)
ASSERT_VI_LOCKED(a->a_vp);
ASSERT_VOP_LOCKED(a->a_vp, "VOP_UNLOCK");
Since the LK_INTERLOCK flag is passed to VOP_UNLOCK() and
vop_unlock_pre(), we test the VI_LOCKED assertion. We get into
trouble with ASSERT_VOP_LOCKED, though, because ASSERT_VOP_LOCKED()
calls VOP_ISLOCKED(), which contains the code:
a.a_desc = VDESC(vop_islocked);
a.a_vp = vp;
a.a_td = td;
ASSERT_VI_UNLOCKED(vp);
We'll definitely blow up here because we're making the exact opposite
assertion.
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