qemu-img: fix in-flight count for qemu-img bench

With aio=native (qemu-img bench -n) one or more requests can be completed
when a new request is submitted.  This in turn can cause bench_cb to
recurse before b->in_flight is updated.  This causes multiple I/Os
to be submitted with the same offset and, furthermore, the blk_aio_*
coroutines are never freed and qemu-img aborts.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/qemu-img.c b/qemu-img.c
index 6949b73..5df66fe 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3559,20 +3559,23 @@ static void bench_cb(void *opaque, int ret)
     }
 
     while (b->n > b->in_flight && b->in_flight < b->nrreq) {
+        int64_t offset = b->offset;
+        /* blk_aio_* might look for completed I/Os and kick bench_cb
+         * again, so make sure this operation is counted by in_flight
+         * and b->offset is ready for the next submission.
+         */
+        b->in_flight++;
+        b->offset += b->step;
+        b->offset %= b->image_size;
         if (b->write) {
-            acb = blk_aio_pwritev(b->blk, b->offset, b->qiov, 0,
-                                  bench_cb, b);
+            acb = blk_aio_pwritev(b->blk, offset, b->qiov, 0, bench_cb, b);
         } else {
-            acb = blk_aio_preadv(b->blk, b->offset, b->qiov, 0,
-                                 bench_cb, b);
+            acb = blk_aio_preadv(b->blk, offset, b->qiov, 0, bench_cb, b);
         }
         if (!acb) {
             error_report("Failed to issue request");
             exit(EXIT_FAILURE);
         }
-        b->in_flight++;
-        b->offset += b->step;
-        b->offset %= b->image_size;
     }
 }