sheepdog: make sure we don't free aiocb before sending all requests

This patch increments the pending counter before sending requests, and
make sures that aiocb is not freed while sending them.
Signed-off-by: NMORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/sheepdog.c

@@ -260,7 +260,6 @@ typedef struct AIOReq {
     uint32_t id;
 
     QLIST_ENTRY(AIOReq) outstanding_aio_siblings;
-    QLIST_ENTRY(AIOReq) aioreq_siblings;
 } AIOReq;
 
 enum AIOCBState {
@@ -283,8 +282,7 @@ struct SheepdogAIOCB {
     void (*aio_done_func)(SheepdogAIOCB *);
 
     int canceled;
-
-    QLIST_HEAD(aioreq_head, AIOReq) aioreq_head;
+    int nr_pending;
 };
 
 typedef struct BDRVSheepdogState {
@@ -388,19 +386,19 @@ static inline AIOReq *alloc_aio_req(BDRVSheepdogState *s, SheepdogAIOCB *acb,
 
     QLIST_INSERT_HEAD(&s->outstanding_aio_head, aio_req,
                       outstanding_aio_siblings);
-    QLIST_INSERT_HEAD(&acb->aioreq_head, aio_req, aioreq_siblings);
 
+    acb->nr_pending++;
     return aio_req;
 }
 
-static inline int free_aio_req(BDRVSheepdogState *s, AIOReq *aio_req)
+static inline void free_aio_req(BDRVSheepdogState *s, AIOReq *aio_req)
 {
     SheepdogAIOCB *acb = aio_req->aiocb;
+
     QLIST_REMOVE(aio_req, outstanding_aio_siblings);
-    QLIST_REMOVE(aio_req, aioreq_siblings);
     g_free(aio_req);
 
-    return !QLIST_EMPTY(&acb->aioreq_head);
+    acb->nr_pending--;
 }
 
 static void coroutine_fn sd_finish_aiocb(SheepdogAIOCB *acb)
@@ -446,7 +444,7 @@ static SheepdogAIOCB *sd_aio_setup(BlockDriverState *bs, QEMUIOVector *qiov,
     acb->canceled = 0;
     acb->coroutine = qemu_coroutine_self();
     acb->ret = 0;
-    QLIST_INIT(&acb->aioreq_head);
+    acb->nr_pending = 0;
     return acb;
 }
 
@@ -663,7 +661,7 @@ static void coroutine_fn send_pending_req(BDRVSheepdogState *s, uint64_t oid, ui
         if (ret < 0) {
             error_report("add_aio_request is failed");
             free_aio_req(s, aio_req);
-            if (QLIST_EMPTY(&acb->aioreq_head)) {
+            if (!acb->nr_pending) {
                 sd_finish_aiocb(acb);
             }
         }
@@ -684,7 +682,6 @@ static void coroutine_fn aio_read_response(void *opaque)
     int ret;
     AIOReq *aio_req = NULL;
     SheepdogAIOCB *acb;
-    int rest;
     unsigned long idx;
 
     if (QLIST_EMPTY(&s->outstanding_aio_head)) {
@@ -755,8 +752,8 @@ static void coroutine_fn aio_read_response(void *opaque)
         error_report("%s", sd_strerror(rsp.result));
     }
 
-    rest = free_aio_req(s, aio_req);
-    if (!rest) {
+    free_aio_req(s, aio_req);
+    if (!acb->nr_pending) {
         /*
          * We've finished all requests which belong to the AIOCB, so
          * we can switch back to sd_co_readv/writev now.
@@ -1568,6 +1565,12 @@ static int coroutine_fn sd_co_rw_vector(void *p)
         }
     }
 
+    /*
+     * Make sure we don't free the aiocb before we are done with all requests.
+     * This additional reference is dropped at the end of this function.
+     */
+    acb->nr_pending++;
+
     while (done != total) {
         uint8_t flags = 0;
         uint64_t old_oid = 0;
@@ -1636,7 +1639,7 @@ static int coroutine_fn sd_co_rw_vector(void *p)
         done += len;
     }
 out:
-    if (QLIST_EMPTY(&acb->aioreq_head)) {
+    if (!--acb->nr_pending) {
         return acb->ret;
     }
     return 1;