scsi: do not call transfer_data after canceling a request

Otherwise, if cancellation is "faked" by the AIO layer and goes
through qemu_aio_flush, the whole request is completed synchronously
during scsi_req_cancel.

Using the enqueued flag would work here, but not in the next patches,
so I'm introducing a new io_canceled flag.  That's because scsi_req_data
is a synchronous callback and the enqueued flag might be reset by the
time it returns.  scsi-disk cannot unref the request until after calling
scsi_req_data.

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

hw/scsi-bus.c

@@ -1107,8 +1107,12 @@ void scsi_req_continue(SCSIRequest *req)
    Once it completes, calling scsi_req_continue will restart I/O.  */
 void scsi_req_data(SCSIRequest *req, int len)
 {
-    trace_scsi_req_data(req->dev->id, req->lun, req->tag, len);
-    req->bus->info->transfer_data(req, len);
+    if (req->io_canceled) {
+        trace_scsi_req_data_canceled(req->dev->id, req->lun, req->tag, len);
+    } else {
+        trace_scsi_req_data(req->dev->id, req->lun, req->tag, len);
+        req->bus->info->transfer_data(req, len);
+    }
 }
 
 void scsi_req_print(SCSIRequest *req)
@@ -1173,11 +1177,15 @@ void scsi_req_complete(SCSIRequest *req, int status)
 
 void scsi_req_cancel(SCSIRequest *req)
 {
-    if (req->ops->cancel_io) {
-        req->ops->cancel_io(req);
+    if (!req->enqueued) {
+        return;
     }
     scsi_req_ref(req);
     scsi_req_dequeue(req);
+    req->io_canceled = true;
+    if (req->ops->cancel_io) {
+        req->ops->cancel_io(req);
+    }
     if (req->bus->info->cancel) {
         req->bus->info->cancel(req);
     }
@@ -1186,10 +1194,17 @@ void scsi_req_cancel(SCSIRequest *req)
 
 void scsi_req_abort(SCSIRequest *req, int status)
 {
+    if (!req->enqueued) {
+        return;
+    }
+    scsi_req_ref(req);
+    scsi_req_dequeue(req);
+    req->io_canceled = true;
     if (req->ops->cancel_io) {
         req->ops->cancel_io(req);
     }
     scsi_req_complete(req, status);
+    scsi_req_unref(req);
 }
 
 void scsi_device_purge_requests(SCSIDevice *sdev, SCSISense sense)

hw/scsi.h

@@ -51,6 +51,7 @@ struct SCSIRequest {
     uint8_t sense[SCSI_SENSE_BUF_SIZE];
     uint32_t sense_len;
     bool enqueued;
+    bool io_canceled;
     void *hba_private;
     QTAILQ_ENTRY(SCSIRequest) next;
 };

trace-events

@@ -278,6 +278,7 @@ usb_host_claim_port(int bus, int hub, int port) "bus %d, hub addr %d, port %d"
 # hw/scsi-bus.c
 scsi_req_alloc(int target, int lun, int tag) "target %d lun %d tag %d"
 scsi_req_data(int target, int lun, int tag, int len) "target %d lun %d tag %d len %d"
+scsi_req_data_canceled(int target, int lun, int tag, int len) "target %d lun %d tag %d len %d"
 scsi_req_dequeue(int target, int lun, int tag) "target %d lun %d tag %d"
 scsi_req_continue(int target, int lun, int tag) "target %d lun %d tag %d"
 scsi_req_parsed(int target, int lun, int tag, int cmd, int mode, int xfer) "target %d lun %d tag %d command %d dir %d length %d"