From 42d56a7bacc5c9297f0d30f182f6f9fc9e4fd8a5 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sun, 8 Sep 2019 16:34:41 -0700
Subject: [PATCH] ircd::ctx: Fix inconsistent refcount() behavior.

---
 include/ircd/ctx/when.h |  9 ++++++---
 ircd/ctx.cc             | 31 ++++++++++++++++++-------------
 2 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/include/ircd/ctx/when.h b/include/ircd/ctx/when.h
index 708faca82..71eb46c91 100644
--- a/include/ircd/ctx/when.h
+++ b/include/ircd/ctx/when.h
@@ -80,7 +80,8 @@ ircd::ctx::when_any(it first,
 		if(is(state(closure(first)), future_state::PENDING))
 			when::set_any_then(p, first, closure);
 
-	if(promise<it>::refcount(p.state()) <= 1)
+	assert(promise<it>::refcount(p) >= 1);
+	if(promise<it>::refcount(p) == 1)
 		p.set_value(last);
 
 	return ret;
@@ -118,7 +119,8 @@ ircd::ctx::when_all(it first,
 		if(is(state(closure(first)), future_state::PENDING))
 			when::set_all_then(p, first, closure);
 
-	if(promise<void>::refcount(p.state()) <= 1)
+	assert(promise<void>::refcount(p) >= 1);
+	if(promise<void>::refcount(p) == 1)
 		p.set_value();
 
 	return ret;
@@ -174,7 +176,8 @@ ircd::ctx::when::all_then(promise<void> &p)
 	if(!p.valid())
 		return;
 
-	if(promise<void>::refcount(p.state()) < 2)
+	assert(promise<void>::refcount(p) >= 1);
+	if(promise<void>::refcount(p) == 1)
 		return p.set_value();
 
 	return p.remove();
diff --git a/ircd/ctx.cc b/ircd/ctx.cc
index f14ce4c00..b9e35d313 100644
--- a/ircd/ctx.cc
+++ b/ircd/ctx.cc
@@ -1989,10 +1989,7 @@ noexcept
 ircd::ctx::promise_base::~promise_base()
 noexcept
 {
-	if(!valid())
-		return;
-
-	if(promise_base::refcount(state()) == 1)
+	if(promise_base::refcount(*this) == 1)
 		set_exception(make_exception_ptr<broken_promise>());
 
 	remove();
@@ -2024,10 +2021,18 @@ ircd::ctx::promise_base::remove()
 void
 ircd::ctx::promise_base::make_ready()
 {
+	const critical_assertion ca;
+
 	assert(valid());
+	promise_base *p
+	{
+		promise_base::head(*this)
+	};
+
+	assert(p);
 	shared_state_base *next
 	{
-		shared_state_base::head(*this)
+		shared_state_base::head(*p)
 	};
 
 	// First we have to chase the linked list of promises reachable
@@ -2110,7 +2115,7 @@ ircd::ctx::promise_base::head(const promise_base &p)
 {
 	return p.st && head(*p.st)?
 		head(*p.st):
-		nullptr;
+		std::addressof(p);
 }
 
 const ircd::ctx::promise_base *
@@ -2409,11 +2414,10 @@ noexcept
 		shared_state_base::refcount(*this)
 	};
 
-	assert(refcount >= 1);
-	if(refcount <= 1)
+	if(refcount == 1)
 		invalidate_promises(*this);
-
-	remove(*this);
+	else if(refcount > 1)
+		remove(*this);
 }
 
 //
@@ -2425,6 +2429,9 @@ size_t
 ircd::ctx::shared_state_base::refcount(const shared_state_base &st)
 {
 	size_t ret{0};
+	if(!is(st, future_state::PENDING))
+		return ret;
+
 	for(const auto *next(head(st)); next; next = next->next)
 		++ret;
 
@@ -2509,9 +2516,7 @@ ircd::ctx::remove(shared_state_base &st)
 		else
 			invalidate_promises(st);
 	}
-
-	assert(last);
-	for(auto *next(last->next); next; last = next, next = next->next)
+	else for(auto *next(last->next); next; last = next, next = next->next)
 		if(next == &st)
 		{
 			last->next = next->next;