[Qemu-devel] [PATCH 1/3] block: Don't wait serialising for non-COR read requests

[Fam Zheng <famz@redhat.com>]

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>
---
 block/backup.c        |  2 +-
 block/io.c            | 12 +++++++-----
 include/block/block.h |  4 ++--
 trace-events          |  2 +-
 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"
-- 
2.4.3