for order := range stackpool {
		lock(&stackpool[order].item.mu)
		list := &stackpool[order].item.span
		for s := list.first; s != nil; {
			next := s.next
			if s.allocCount == 0 {
				list.remove(s)
				s.manualFreeList = 0
				osStackFree(s)
				mheap_.freeManual(s, spanAllocStack)
			}
			s = next
		}
		unlock(&stackpool[order].item.mu)
	}

  root
# Anything that can grow the stack can acquire STACKGROW.
# (Most higher layers imply STACKGROW, like MALLOC.)
< STACKGROW
# Below STACKGROW is the stack allocator/copying implementation.
< gscan;
gscan < stackpool;
gscan < stackLarge;
# Generally, hchan must be acquired before gscan. But in one case,
# where we suspend a G and then shrink its stack, syncadjustsudogs
# can acquire hchan locks while holding gscan. To allow this case,

	lockRankProfBlock:       "profBlock",
	lockRankProfMemActive:   "profMemActive",
	lockRankProfMemFuture:   "profMemFuture",
	lockRankGscan:           "gscan",
	lockRankStackpool:       "stackpool",
	lockRankStackLarge:      "stackLarge",
	lockRankHchanLeaf:       "hchanLeaf",
	lockRankWbufSpans:       "wbufSpans",
	lockRankMheap:           "mheap",
	lockRankMheapSpecial:    "mheapSpecial",

REGISTER_NO_GRADIENT_OP("QueueDequeueUpTo");
REGISTER_NO_GRADIENT_OP("QueueClose");
REGISTER_NO_GRADIENT_OP("QueueSize");
REGISTER_NO_GRADIENT_OP("Stack");
REGISTER_NO_GRADIENT_OP("StackPush");
REGISTER_NO_GRADIENT_OP("StackPop");
REGISTER_NO_GRADIENT_OP("StackClose");
REGISTER_NO_GRADIENT_OP("GetSessionHandle");
REGISTER_NO_GRADIENT_OP("GetSessionHandleV2");
REGISTER_NO_GRADIENT_OP("GetSessionTensor");