block: Don't wait serialising for non-COR read requests

The assertion problem was noticed in 06c3916b35a, but it wasn't
completely fixed, because even though the req is not marked as
serialising, it still gets serialised by wait_serialising_requests
against other serialising requests, which could lead to the same
assertion failure.

Fix it by even more explicitly skipping the serialising for this
specific case.

Signed-off-by: Fam Zheng <famz@redhat.com>
Message-id: 1448962590-2842-2-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

4 files changed, 11 insertions, 9 deletions

diff --git a/block/backup.c b/block/backup.c
index 3b39119..705bb77 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -132,7 +132,7 @@ static int coroutine_fn backup_do_cow(BlockDriverState *bs,
         qemu_iovec_init_external(&bounce_qiov, &iov, 1);
 
         if (is_write_notifier) {
-            ret = bdrv_co_no_copy_on_readv(bs,
+            ret = bdrv_co_readv_no_serialising(bs,
                                            start * BACKUP_SECTORS_PER_CLUSTER,
                                            n, &bounce_qiov);
         } else {
diff --git a/block/io.c b/block/io.c
index adc1eab..e00fb5d 100644
--- a/block/io.c
+++ b/block/io.c
@@ -863,7 +863,9 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
         mark_request_serialising(req, bdrv_get_cluster_size(bs));
     }
 
-    wait_serialising_requests(req);
+    if (!(flags & BDRV_REQ_NO_SERIALISING)) {
+        wait_serialising_requests(req);
+    }
 
     if (flags & BDRV_REQ_COPY_ON_READ) {
         int pnum;
@@ -952,7 +954,7 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
     }
 
     /* Don't do copy-on-read if we read data before write operation */
-    if (bs->copy_on_read && !(flags & BDRV_REQ_NO_COPY_ON_READ)) {
+    if (bs->copy_on_read && !(flags & BDRV_REQ_NO_SERIALISING)) {
         flags |= BDRV_REQ_COPY_ON_READ;
     }
 
@@ -1021,13 +1023,13 @@ int coroutine_fn bdrv_co_readv(BlockDriverState *bs, int64_t sector_num,
     return bdrv_co_do_readv(bs, sector_num, nb_sectors, qiov, 0);
 }
 
-int coroutine_fn bdrv_co_no_copy_on_readv(BlockDriverState *bs,
+int coroutine_fn bdrv_co_readv_no_serialising(BlockDriverState *bs,
     int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
 {
-    trace_bdrv_co_no_copy_on_readv(bs, sector_num, nb_sectors);
+    trace_bdrv_co_readv_no_serialising(bs, sector_num, nb_sectors);
 
     return bdrv_co_do_readv(bs, sector_num, nb_sectors, qiov,
-                            BDRV_REQ_NO_COPY_ON_READ);
+                            BDRV_REQ_NO_SERIALISING);
 }
 
 int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
diff --git a/include/block/block.h b/include/block/block.h
index 73edb1a..3477328 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -61,7 +61,7 @@ typedef enum {
      * opened with BDRV_O_UNMAP.
      */
     BDRV_REQ_MAY_UNMAP          = 0x4,
-    BDRV_REQ_NO_COPY_ON_READ    = 0x8,
+    BDRV_REQ_NO_SERIALISING     = 0x8,
 } BdrvRequestFlags;
 
 typedef struct BlockSizes {
@@ -248,7 +248,7 @@ int coroutine_fn bdrv_co_readv(BlockDriverState *bs, int64_t sector_num,
     int nb_sectors, QEMUIOVector *qiov);
 int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
     int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
-int coroutine_fn bdrv_co_no_copy_on_readv(BlockDriverState *bs,
+int coroutine_fn bdrv_co_readv_no_serialising(BlockDriverState *bs,
     int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
 int coroutine_fn bdrv_co_writev(BlockDriverState *bs, int64_t sector_num,
     int nb_sectors, QEMUIOVector *qiov);
diff --git a/trace-events b/trace-events
index 0b0ff02..2fce98e 100644
--- a/trace-events
+++ b/trace-events
@@ -69,7 +69,7 @@ bdrv_aio_write_zeroes(void *bs, int64_t sector_num, int nb_sectors, int flags, v
 bdrv_lock_medium(void *bs, bool locked) "bs %p locked %d"
 bdrv_co_readv(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
 bdrv_co_copy_on_readv(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
-bdrv_co_no_copy_on_readv(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
+bdrv_co_readv_no_serialising(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
 bdrv_co_writev(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
 bdrv_co_write_zeroes(void *bs, int64_t sector_num, int nb_sector, int flags) "bs %p sector_num %"PRId64" nb_sectors %d flags %#x"
 bdrv_co_io_em(void *bs, int64_t sector_num, int nb_sectors, int is_write, void *acb) "bs %p sector_num %"PRId64" nb_sectors %d is_write %d acb %p"