Commit 539343c0 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by John Snow
Browse files

dma-helpers: ensure AIO callback is invoked after cancellation 



dma_aio_cancel unschedules the BH if there is one, which corresponds
to the reschedule_dma case of dma_blk_cb.  This can stall the DMA
permanently, because dma_complete will never get invoked and therefore
nobody will ever invoke the original AIO callback in dbs->common.cb.

Fix this by invoking the callback (which is ensured to happen after
a bdrv_aio_cancel_async, or done manually in the dbs->bh case), and
add assertions to check that the DMA state machine is indeed waiting
for dma_complete or reschedule_dma, but never both.

Reported-by: default avatarJohn Snow <jsnow@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-id: 20190729213416.1972-1-pbonzini@redhat.com
Signed-off-by: default avatarJohn Snow <jsnow@redhat.com>
parent afd76053

dma-helpers.c

+9 −4
Original line number Diff line number Diff line
@@ -90,6 +90,7 @@ static void reschedule_dma(void *opaque) 
{

    DMAAIOCB *dbs = (DMAAIOCB *)opaque;



    assert(!dbs->acb && dbs->bh);

    qemu_bh_delete(dbs->bh);

    dbs->bh = NULL;

    dma_blk_cb(dbs, 0);
@@ -111,15 +112,12 @@ static void dma_complete(DMAAIOCB *dbs, int ret) 
{

    trace_dma_complete(dbs, ret, dbs->common.cb);



    assert(!dbs->acb && !dbs->bh);

    dma_blk_unmap(dbs);

    if (dbs->common.cb) {

        dbs->common.cb(dbs->common.opaque, ret);

    }

    qemu_iovec_destroy(&dbs->iov);

    if (dbs->bh) {

        qemu_bh_delete(dbs->bh);

        dbs->bh = NULL;

    }

    qemu_aio_unref(dbs);

}
@@ -179,14 +177,21 @@ static void dma_aio_cancel(BlockAIOCB *acb) 


    trace_dma_aio_cancel(dbs);



    assert(!(dbs->acb && dbs->bh));

    if (dbs->acb) {

        /* This will invoke dma_blk_cb.  */

        blk_aio_cancel_async(dbs->acb);

        return;

    }



    if (dbs->bh) {

        cpu_unregister_map_client(dbs->bh);

        qemu_bh_delete(dbs->bh);

        dbs->bh = NULL;

    }

    if (dbs->common.cb) {

        dbs->common.cb(dbs->common.opaque, -ECANCELED);

    }

}



static AioContext *dma_get_aio_context(BlockAIOCB *acb)