[Qemu-devel] [PULL 06/21] qcow2: qcow2_co_preadv: improve locking

[Max Reitz <mreitz@redhat.com>]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

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 <vsementsov@virtuozzo.com>
Message-id: 20190506142741.41731-7-vsementsov@virtuozzo.com
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 1413df1389..4a89850389 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1969,8 +1969,6 @@ 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 */
@@ -1980,7 +1978,9 @@ 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;
         }
@@ -1995,10 +1995,8 @@ 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;
                 }
@@ -2014,11 +2012,9 @@ 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;
             }
@@ -2055,11 +2051,9 @@ 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;
             }
@@ -2094,8 +2088,6 @@ 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);
 
-- 
2.21.0