[Qemu-devel] [PATCH] qemu-coroutine-lock: fix co_queue multi-adding bug

[w00214312]

From: Bin Wu <address@hidden>

When a coroutine holds a lock, other coroutines who want to get
the lock must wait on a co_queue by adding themselves to the
CoQueue. However, if a waiting coroutine is woken up with the
lock still be holding by other coroutine, this waiting coroutine
will add itself to the co_queue again. Latter, when the lock
is released, a coroutine re-enter will occur.

We need to determine whether a coroutine is alread in the co_queue
before adding it to the waiting queue.

Signed-off-by: Bin Wu <address@hidden>
---
 include/block/coroutine_int.h | 1 +
 qemu-coroutine-lock.c         | 6 +++++-
 qemu-coroutine.c              | 1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/block/coroutine_int.h b/include/block/coroutine_int.h
index f133d65..c524990 100644
--- a/include/block/coroutine_int.h
+++ b/include/block/coroutine_int.h
@@ -42,6 +42,7 @@ struct Coroutine {
     /* Coroutines that should be woken up when we yield or terminate */
     QTAILQ_HEAD(, Coroutine) co_queue_wakeup;
     QTAILQ_ENTRY(Coroutine) co_queue_next;
+    bool in_co_queue;
 };
 
 Coroutine *qemu_coroutine_new(void);
diff --git a/qemu-coroutine-lock.c b/qemu-coroutine-lock.c
index e4860ae..d256f53 100644
--- a/qemu-coroutine-lock.c
+++ b/qemu-coroutine-lock.c
@@ -36,7 +36,10 @@ void qemu_co_queue_init(CoQueue *queue)
 void coroutine_fn qemu_co_queue_wait(CoQueue *queue)
 {
     Coroutine *self = qemu_coroutine_self();
-    QTAILQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
+    if (!self->in_co_queue) {
+        QTAILQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
+        self->in_co_queue = true;
+    }
     qemu_coroutine_yield();
     assert(qemu_in_coroutine());
 }
@@ -71,6 +74,7 @@ static bool qemu_co_queue_do_restart(CoQueue *queue, bool 
single)
 
     while ((next = QTAILQ_FIRST(&queue->entries)) != NULL) {
         QTAILQ_REMOVE(&queue->entries, next, co_queue_next);
+        next->in_co_queue = false;
         QTAILQ_INSERT_TAIL(&self->co_queue_wakeup, next, co_queue_next);
         trace_qemu_co_queue_next(next);
         if (single) {
diff --git a/qemu-coroutine.c b/qemu-coroutine.c
index 525247b..a103721 100644
--- a/qemu-coroutine.c
+++ b/qemu-coroutine.c
@@ -75,6 +75,7 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
     }
 
     co->entry = entry;
+    co->in_co_queue = false;
     QTAILQ_INIT(&co->co_queue_wakeup);
     return co;
 }
-- 
1.7.12.4