[Qemu-devel] [PATCH v6 6/8] qcow2: qcow2_co_preadv: improve locking

[Vladimir Sementsov-Ogievskiy]

Background: decryption will be done in threads, to take benefit of it,
we should move it out of the lock first.

But let's go further: it turns out, that only
qcow2_get_cluster_offset() needs locking, so reduce locking to it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
 block/qcow2.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 7970d0992a..5954696245 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1970,8 +1970,6 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState 
*bs, uint64_t offset,
 
     qemu_iovec_init(&hd_qiov, qiov->niov);
 
-    qemu_co_mutex_lock(&s->lock);
-
     while (bytes != 0) {
 
         /* prepare next request */
@@ -1981,7 +1979,9 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState 
*bs, uint64_t offset,
                             QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
         }
 
+        qemu_co_mutex_lock(&s->lock);
         ret = qcow2_get_cluster_offset(bs, offset, &cur_bytes, 
&cluster_offset);
+        qemu_co_mutex_unlock(&s->lock);
         if (ret < 0) {
             goto fail;
         }
@@ -1996,10 +1996,8 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState 
*bs, uint64_t offset,
 
             if (bs->backing) {
                 BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING_AIO);
-                qemu_co_mutex_unlock(&s->lock);
                 ret = bdrv_co_preadv(bs->backing, offset, cur_bytes,
                                      &hd_qiov, 0);
-                qemu_co_mutex_lock(&s->lock);
                 if (ret < 0) {
                     goto fail;
                 }
@@ -2015,11 +2013,9 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState 
*bs, uint64_t offset,
             break;
 
         case QCOW2_CLUSTER_COMPRESSED:
-            qemu_co_mutex_unlock(&s->lock);
             ret = qcow2_co_preadv_compressed(bs, cluster_offset,
                                              offset, cur_bytes,
                                              &hd_qiov);
-            qemu_co_mutex_lock(&s->lock);
             if (ret < 0) {
                 goto fail;
             }
@@ -2056,11 +2052,9 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState 
*bs, uint64_t offset,
             }
 
             BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
-            qemu_co_mutex_unlock(&s->lock);
             ret = bdrv_co_preadv(s->data_file,
                                  cluster_offset + offset_in_cluster,
                                  cur_bytes, &hd_qiov, 0);
-            qemu_co_mutex_lock(&s->lock);
             if (ret < 0) {
                 goto fail;
             }
@@ -2095,8 +2089,6 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState 
*bs, uint64_t offset,
     ret = 0;
 
 fail:
-    qemu_co_mutex_unlock(&s->lock);
-
     qemu_iovec_destroy(&hd_qiov);
     qemu_vfree(cluster_data);
 
-- 
2.18.0