block/file-posix: don't use functions calling AIO_WAIT_WHILE in worker threads

When calling bdrv_getlength() in handle_aiocb_write_zeroes(), the
function creates a new coroutine and then waits that it finishes using
AIO_WAIT_WHILE.
The problem is that this function could also run in a worker thread,
that has a different AioContext from main loop and iothreads, therefore
in AIO_WAIT_WHILE we will have in_aio_context_home_thread(ctx) == false
and therefore
assert(qemu_get_current_aio_context() == qemu_get_aio_context());
in the else branch will fail, crashing QEMU.

Aside from that, bdrv_getlength() is wrong also conceptually, because
it reads the BDS graph from another thread and is not protected by
any lock.

Replace it with raw_co_getlength, that doesn't create a coroutine and
doesn't read the BDS graph.

Reported-by: Ninad Palsule <ninad@linux.vnet.ibm.com>
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20230209154522.1164401-1-eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/file-posix.c b/block/file-posix.c
index d3073a7..9a99111 100644 (file)
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1738,7 +1738,7 @@ static int handle_aiocb_write_zeroes(void *opaque)
 #ifdef CONFIG_FALLOCATE
     /* Last resort: we are trying to extend the file with zeroed data. This
      * can be done via fallocate(fd, 0) */
-    len = bdrv_getlength(aiocb->bs);
+    len = raw_co_getlength(aiocb->bs);
     if (s->has_fallocate && len >= 0 && aiocb->aio_offset >= len) {
         int ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes);
         if (ret == 0 || ret != -ENOTSUP) {