block: Honor blk_set_aio_context() context requirements

The documentation for bdrv_set_aio_context_ignore() states this:

 * The caller must own the AioContext lock for the old AioContext of bs, but it
 * must not own the AioContext lock for new_context (unless new_context is the
 * same as the current context of bs).

As blk_set_aio_context() makes use of this function, this rule also
applies to it.

Fix all occurrences where this rule wasn't honored.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Sergio Lopez <slp@redhat.com>
Message-Id: <20201214170519.223781-2-slp@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c
index 71c337c7b7..3675f8deaf 100644
--- a/hw/block/dataplane/xen-block.c
+++ b/hw/block/dataplane/xen-block.c
@@ -725,6 +725,7 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
 {
     ERRP_GUARD();
     XenDevice *xendev = dataplane->xendev;
+    AioContext *old_context;
     unsigned int ring_size;
     unsigned int i;
 
@@ -808,10 +809,14 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
         goto stop;
     }
 
-    aio_context_acquire(dataplane->ctx);
+    old_context = blk_get_aio_context(dataplane->blk);
+    aio_context_acquire(old_context);
     /* If other users keep the BlockBackend in the iothread, that's ok */
     blk_set_aio_context(dataplane->blk, dataplane->ctx, NULL);
+    aio_context_release(old_context);
+
     /* Only reason for failure is a NULL channel */
+    aio_context_acquire(dataplane->ctx);
     xen_device_set_event_channel_context(xendev, dataplane->event_channel,
                                          dataplane->ctx, &error_abort);
     aio_context_release(dataplane->ctx);