features/qemu-block: simplify coroutine model to use single synctask, ucontext

The current coroutine model, mapping synctasks 1-1 with qemu internal
Coroutines, has some unresolved raciness issues. This problem usually
manifests as lifecycle mismatches between top-level (gluster created)
synctasks and the subsequently created internal coroutines from that
context. Qemu's internal queueing (and locking) can cause situations
where the top-level synctask is destroyed before the internal scheduler
has released references to memory, leading to use after free crashes
and asserts.

Simplify the coroutine model to use a single synctask as a coroutine
processor and rely on the existing native ucontext coroutine
implementation. The syncenv thread is donated to qemu and ensures a
single top-level coroutine is processed at a time. Qemu now has
complete control over coroutine scheduling.

BUG: 986775
Change-Id: I38223479a608d80353128e390f243933fc946fd6
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-on: http://review.gluster.org/6110
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 0 insertions, 51 deletions

diff --git a/xlators/features/qemu-block/src/coroutine-synctask.h b/xlators/features/qemu-block/src/coroutine-synctask.h
deleted file mode 100644
index 0f0aa99cc..000000000
--- a/xlators/features/qemu-block/src/coroutine-synctask.h
+++ /dev/null
@@ -1,51 +0,0 @@
-/*
-  Copyright (c) 2013 Red Hat, Inc. <http://www.redhat.com>
-  This file is part of GlusterFS.
-
-  This file is licensed to you under your choice of the GNU Lesser
-  General Public License, version 3 or any later version (LGPLv3 or
-  later), or the GNU General Public License, version 2 (GPLv2), in all
-  cases as published by the Free Software Foundation.
-*/
-
-#ifndef __COROUTINE_SYNCTASK_H
-#define __COROUTINE_SYNCTASK_H
-
-#include "syncop.h"
-#include "block/coroutine_int.h"
-#include "qemu-common.h"
-#include "block/coroutine_int.h"
-
-/*
-  Three entities:
-
-  synctask - glusterfs implementation of xlator friendly lightweight threads
-  Coroutine - qemu coroutine API for its block drivers
-  CoroutineSynctask - implementation of Coroutine using synctasks
-
-  Coroutine is an "embedded" structure inside CoroutineSynctask, called "base".
-
-  E.g:
-
-  Coroutine *co;
-  CoroutineSynctask *cs;
-  struct synctask *synctask;
-
-  cs == synctask->opaque;
-  co == &(cs->base);
-  cs = DO_UPCAST(CoroutineSynctask, base, co);
-  synctask == cs->synctask;
-
-*/
-
-typedef struct {
-	Coroutine base;
-	struct synctask *synctask;
-	CoroutineAction action;
-	bool run;
-	bool die;
-} CoroutineSynctask;
-
-
-
-#endif /* !__COROUTINE_SYNCTASK_H */