block: Handle multiwrite errors only when all requests have completed

Don't try to be clever by freeing all temporary data and calling all callbacks
when the return value (an error) is certain. Doing so has at least two
important problems:

* The temporary data that is freed (qiov, possibly zero buffer) is still used
  by the requests that have not yet completed.
* Calling the callbacks for all requests in the multiwrite means for the caller
  that it may free buffers etc. which are still in use.

Just remember the error value and do the cleanup when all requests have
completed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit de189a1b4a471d37a2909e97646654fc9751b52f)

diff --git a/block.c b/block.c
index 80f2faecdb5701ccad857b919081868069227129..1694780467185c2d8bf58ae3ef8d48ae1c6d03df 100644 (file)
--- a/block.c
+++ b/block.c
@@ -1661,14 +1661,11 @@ static void multiwrite_cb(void *opaque, int ret)
 
     if (ret < 0 && !mcb->error) {
         mcb->error = ret;
-        multiwrite_user_cb(mcb);
     }
 
     mcb->num_requests--;
     if (mcb->num_requests == 0) {
-        if (mcb->error == 0) {
-            multiwrite_user_cb(mcb);
-        }
+        multiwrite_user_cb(mcb);
         qemu_free(mcb);
     }
 }