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[Qemu-devel] [PATCH v3 1/4] block: disallow BDRV_REQ_NO_SERIALISING for
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
[Qemu-devel] [PATCH v3 1/4] block: disallow BDRV_REQ_NO_SERIALISING for write |
Date: |
Thu, 5 Jul 2018 10:46:35 +0300 |
Before commit 9ded4a01149 "backup: Use copy offloading",
BDRV_REQ_NO_SERIALISING was used for only one case: read in
copy-on-write operation during backup. Also, the flag was handled only
on read path (in bdrv_co_preadv and bdrv_aligned_preadv).
After 9ded4a01149, flag is used for not waiting serializing operations
on backup target (in same case of copy-on-write operation). This
behavior change is unsubstantiated and potentially dangerous, let's
drop it.
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
include/block/block.h | 13 +++++++++++++
block/io.c | 7 ++++++-
2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/include/block/block.h b/include/block/block.h
index e5c7759a0c..a06a4d27de 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -50,6 +50,19 @@ typedef enum {
* opened with BDRV_O_UNMAP.
*/
BDRV_REQ_MAY_UNMAP = 0x4,
+
+ /* The BDRV_REQ_NO_SERIALISING means that we don't want to
+ * wait_serialising_requests(), when reading.
+ *
+ * This flag is used for backup copy on write operation, when we need to
+ * read old data before write (write notifier triggered). It is ok, due to
+ * we already waited for serializing requests in initiative write (see
+ * bdrv_aligned_pwritev), and it is necessary for the case when initiative
+ * write is serializing itself (we'll dead lock waiting it).
+ *
+ * The described case is the only usage for the flag for now, so, it is
+ * supported only for read operation and restricted for write.
+ */
BDRV_REQ_NO_SERIALISING = 0x8,
BDRV_REQ_FUA = 0x10,
BDRV_REQ_WRITE_COMPRESSED = 0x20,
diff --git a/block/io.c b/block/io.c
index 1a2272fad3..51bef9fc50 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1572,6 +1572,8 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild
*child,
max_transfer = QEMU_ALIGN_DOWN(MIN_NON_ZERO(bs->bl.max_transfer, INT_MAX),
align);
+ /* BDRV_REQ_NO_SERIALISING is only for read operation */
+ assert(!(flags & BDRV_REQ_NO_SERIALISING));
waited = wait_serialising_requests(req);
assert(!waited || !req->serialising);
assert(req->overlap_offset <= offset);
@@ -2931,9 +2933,12 @@ static int coroutine_fn
bdrv_co_copy_range_internal(BdrvChild *src,
bytes, BDRV_TRACKED_WRITE);
if (!(flags & BDRV_REQ_NO_SERIALISING)) {
+ /* BDRV_REQ_NO_SERIALISING is only for read */
wait_serialising_requests(&src_req);
- wait_serialising_requests(&dst_req);
}
+
+ wait_serialising_requests(&dst_req);
+
if (recurse_src) {
ret = src->bs->drv->bdrv_co_copy_range_from(src->bs,
src, src_offset,
--
2.11.1