On Tue, Aug 14, 2012 at 10:29:26AM +0200, Kevin Wolf wrote: > >>> +static void gluster_finish_aiocb(struct glfs_fd *fd, ssize_t ret, void > >>> *arg) > >>> +{ > >>> + GlusterAIOCB *acb = (GlusterAIOCB *)arg; > >>> + BDRVGlusterState *s = acb->common.bs->opaque; > >>> + > >>> + acb->ret = ret; > >>> + if (qemu_gluster_send_pipe(s, acb) < 0) { > >>> + /* > >>> + * Gluster AIO callback thread failed to notify the waiting > >>> + * QEMU thread about IO completion. Nothing much can be done > >>> + * here but to abruptly abort. > >>> + * > >>> + * FIXME: Check if the read side of the fd handler can somehow > >>> + * be notified of this failure paving the way for a graceful > >>> exit. > >>> + */ > >>> + error_report("Gluster failed to notify QEMU about IO > >>> completion"); > >>> + abort(); > >> > >> In the extreme case you may choose to make this disk inaccessible > >> (something like bs->drv = NULL), but abort() kills the whole VM and > >> should only be called when there is a bug. > > > > There have been concerns raised about this earlier too. I settled for this > > since I couldn't see a better way out and I could see the precedence > > for this in posix-aio-compat.c > > > > So I could just do the necessary cleanup, set bs->drv to NULL and return > > from > > here ? But how do I wake up the QEMU thread that is waiting on the read side > > of the pipe ? W/o that, the QEMU thread that waits on the read side of the > > pipe is still hung. > > There is no other thread. But you're right, you should probably > unregister the aio_fd_handler and any other pending callbacks.
As I clarified in the other mail, this (gluster_finish_aiocb) is called from gluster thread context and hence QEMU thread that raised the original read/write request is still blocked on qemu_aio_wait(). I tried the following cleanup instead of abrupt abort: close(read_fd); /* This will wake up the QEMU thread blocked on select(read_fd...) */ close(write_fd); qemu_aio_set_fd_handler(read_fd, NULL, NULL, NULL, NULL); qemu_aio_release(acb); s->qemu_aio_count--; bs->drv = NULL; I tested this by manually injecting faults into qemu_gluster_send_pipe(). With the above cleanup, the guest kernel crashes with IO errors. Is there anything else that I need to do or do differently to retain the VM running w/o disk access ? I thought of completing the aio callback by doing acb->common.cb(acb->common.opaque, -EIO); but that would do a coroutine enter from gluster thread, which I don't think should be done. Regards, Bharata.