[Qemu-devel] [PATCH v2 21/35] scsi-disk: bump SCSIRequest reference count until aio completion runs

[Paolo Bonzini <pbonzini@redhat.com>]

In some cases a request may be canceled before the completion
callback runs.  Keep a reference to the request between starting
an AIO operation, and let scsi_*_complete remove it.

Since scsi_handle_rw_error returns whether something else has to
be done for the request by the caller, it makes sense to transfer
ownership of the ref to scsi_handle_rw_error when it returns 1;
scsi_dma_restart_bh will then free the reference after restarting
the operation.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
        v1->v2: Add "return" after calling scsi_write_complete with
        ENOMEDIUM.  Bump refcount before testing data direction.

 hw/scsi-disk.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c
index e28c39d..702e6ca 100644
--- a/hw/scsi-disk.c
+++ b/hw/scsi-disk.c
@@ -139,6 +139,7 @@ static void scsi_read_complete(void * opaque, int ret)
 
     if (ret) {
         if (scsi_handle_rw_error(r, -ret, SCSI_REQ_STATUS_RETRY_READ)) {
+            /* Leave in ref for scsi_dma_restart_bh.  */
             return;
         }
     }
@@ -149,6 +150,7 @@ static void scsi_read_complete(void * opaque, int ret)
     r->sector += n;
     r->sector_count -= n;
     scsi_req_data(&r->req, r->qiov.size);
+    scsi_req_unref(&r->req);
 }
 
 static void scsi_flush_complete(void * opaque, int ret)
@@ -163,11 +165,13 @@ static void scsi_flush_complete(void * opaque, int ret)
 
     if (ret < 0) {
         if (scsi_handle_rw_error(r, -ret, SCSI_REQ_STATUS_RETRY_FLUSH)) {
+            /* Leave in ref for scsi_dma_restart_bh.  */
             return;
         }
     }
 
     scsi_req_complete(&r->req, GOOD);
+    scsi_req_unref(&r->req);
 }
 
 /* Read more data from scsi device into buffer.  */
@@ -193,6 +197,8 @@ static void scsi_read_data(SCSIRequest *req)
     /* No data transfer may already be in progress */
     assert(r->req.aiocb == NULL);
 
+    /* Save a ref for scsi_read_complete, in case r is canceled.  */
+    scsi_req_ref(&r->req);
     if (r->req.cmd.mode == SCSI_XFER_TO_DEV) {
         DPRINTF("Data transfer direction invalid\n");
         scsi_read_complete(r, -EINVAL);
@@ -201,7 +207,9 @@ static void scsi_read_data(SCSIRequest *req)
 
     if (s->tray_open) {
         scsi_read_complete(r, -ENOMEDIUM);
+        return;
     }
+
     n = scsi_init_iovec(r);
     bdrv_acct_start(s->bs, &r->acct, n * BDRV_SECTOR_SIZE, BDRV_ACCT_READ);
     r->req.aiocb = bdrv_aio_readv(s->bs, r->sector, &r->qiov, n,
@@ -279,6 +287,7 @@ static void scsi_write_complete(void * opaque, int ret)
         DPRINTF("Write complete tag=0x%x more=%d\n", r->req.tag, r->qiov.size);
         scsi_req_data(&r->req, r->qiov.size);
     }
+    scsi_req_unref(&r->req);
 }
 
 static void scsi_write_data(SCSIRequest *req)
@@ -290,6 +299,8 @@ static void scsi_write_data(SCSIRequest *req)
     /* No data transfer may already be in progress */
     assert(r->req.aiocb == NULL);
 
+    /* Save a ref for scsi_write_complete, in case r is canceled.  */
+    scsi_req_ref(&r->req);
     if (r->req.cmd.mode != SCSI_XFER_TO_DEV) {
         DPRINTF("Data transfer direction invalid\n");
         scsi_write_complete(r, -EINVAL);
@@ -300,6 +311,7 @@ static void scsi_write_data(SCSIRequest *req)
     if (n) {
         if (s->tray_open) {
             scsi_write_complete(r, -ENOMEDIUM);
+            return;
         }
         bdrv_acct_start(s->bs, &r->acct, n * BDRV_SECTOR_SIZE, BDRV_ACCT_WRITE);
         r->req.aiocb = bdrv_aio_writev(s->bs, r->sector, &r->qiov, n,
@@ -344,6 +356,8 @@ static void scsi_dma_restart_bh(void *opaque)
                     scsi_req_complete(&r->req, GOOD);
                 }
             }
+            /* This reference was left in by scsi_handle_rw_error.  */
+            scsi_req_unref(&r->req);
         }
     }
 }
@@ -1345,6 +1359,8 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *buf)
         r->iov.iov_len = rc;
         break;
     case SYNCHRONIZE_CACHE:
+        /* Save a ref for scsi_flush_complete, in case r is canceled.  */
+        scsi_req_ref(&r->req);
         bdrv_acct_start(s->bs, &r->acct, 0, BDRV_ACCT_FLUSH);
         r->req.aiocb = bdrv_aio_flush(s->bs, scsi_flush_complete, r);
         if (r->req.aiocb == NULL) {
-- 
1.7.6