block: Fix AioContext locking in bdrv_open_inherit()

bdrv_open_inherit() calls several functions for which it needs to hold
the AioContext lock, but currently doesn't. This includes calls in
bdrv_append_temp_snapshot(), for which bdrv_open_inherit() is the only
caller. Fix the locking in these places.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230605085711.21261-8-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -3794,6 +3794,7 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
     int64_t total_size;
     QemuOpts *opts = NULL;
     BlockDriverState *bs_snapshot = NULL;
+    AioContext *ctx = bdrv_get_aio_context(bs);
     int ret;
 
     GLOBAL_STATE_CODE();
@@ -3802,7 +3803,10 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
        instead of opening 'filename' directly */
 
     /* Get the required size from the image */
+    aio_context_acquire(ctx);
     total_size = bdrv_getlength(bs);
+    aio_context_release(ctx);
+
     if (total_size < 0) {
         error_setg_errno(errp, -total_size, "Could not get image size");
         goto out;
@@ -3836,7 +3840,10 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
         goto out;
     }
 
+    aio_context_acquire(ctx);
     ret = bdrv_append(bs_snapshot, bs, errp);
+    aio_context_release(ctx);
+
     if (ret < 0) {
         bs_snapshot = NULL;
         goto out;
@@ -3880,6 +3887,7 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
     Error *local_err = NULL;
     QDict *snapshot_options = NULL;
     int snapshot_flags = 0;
+    AioContext *ctx = qemu_get_aio_context();
 
     assert(!child_class || !flags);
     assert(!child_class == !parent);
@@ -4017,9 +4025,13 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
             /* Not requesting BLK_PERM_CONSISTENT_READ because we're only
              * looking at the header to guess the image format. This works even
              * in cases where a guest would not see a consistent state. */
-            file = blk_new(bdrv_get_aio_context(file_bs), 0, BLK_PERM_ALL);
+            ctx = bdrv_get_aio_context(file_bs);
+            aio_context_acquire(ctx);
+            file = blk_new(ctx, 0, BLK_PERM_ALL);
             blk_insert_bs(file, file_bs, &local_err);
             bdrv_unref(file_bs);
+            aio_context_release(ctx);
+
             if (local_err) {
                 goto fail;
             }
@@ -4065,8 +4077,13 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
         goto fail;
     }
 
+    /* The AioContext could have changed during bdrv_open_common() */
+    ctx = bdrv_get_aio_context(bs);
+
     if (file) {
+        aio_context_acquire(ctx);
         blk_unref(file);
+        aio_context_release(ctx);
         file = NULL;
     }
 
@@ -4124,13 +4141,16 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
          * (snapshot_bs); thus, we have to drop the strong reference to bs
          * (which we obtained by calling bdrv_new()). bs will not be deleted,
          * though, because the overlay still has a reference to it. */
+        aio_context_acquire(ctx);
         bdrv_unref(bs);
+        aio_context_release(ctx);
         bs = snapshot_bs;
     }
 
     return bs;
 
 fail:
+    aio_context_acquire(ctx);
     blk_unref(file);
     qobject_unref(snapshot_options);
     qobject_unref(bs->explicit_options);
@@ -4139,11 +4159,14 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
     bs->options = NULL;
     bs->explicit_options = NULL;
     bdrv_unref(bs);
+    aio_context_release(ctx);
     error_propagate(errp, local_err);
     return NULL;
 
 close_and_fail:
+    aio_context_acquire(ctx);
     bdrv_unref(bs);
+    aio_context_release(ctx);
     qobject_unref(snapshot_options);
     qobject_unref(options);
     error_propagate(errp, local_err);