Il 02/07/2014 11:46, Gonglei (Arei) ha scritto:
Hi, Paolo. We have tested your above patch, and it works well for us.
I'm still not sure where the fix is. I jotted the patch quickly, but
I'd rather understand it better before submitting it. Here is it again:
--- a/dma-helpers.c
+++ b/dma-helpers.c
@@ -181,15 +181,15 @@ static void dma_aio_cancel(BlockDriverAIOCB *acb)
trace_dma_aio_cancel(dbs);
+ dbs->in_cancel = true;
if (dbs->acb) {
BlockDriverAIOCB *acb = dbs->acb;
dbs->acb = NULL;
- dbs->in_cancel = true;
bdrv_aio_cancel(acb);
- dbs->in_cancel = false;
}
dbs->common.cb = NULL;
dma_complete(dbs, 0);
+ qemu_aio_release(dbs);
}
static const AIOCBInfo dma_aiocb_info = {
and here is dma_complete:
static void dma_complete(DMAAIOCB *dbs, int ret)
{
trace_dma_complete(dbs, ret, dbs->common.cb);
dma_bdrv_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;
}
if (!dbs->in_cancel) {
/* Requests may complete while dma_aio_cancel is in progress.
* this case, the AIOCB should not be released because it is
* still referenced by dma_aio_cancel. */
qemu_aio_release(dbs);
}
}
The qemu_aio_release call obviously happened during the second
dma_complete call.
However, the second dma_complete call does not call the callback, and
even if dma_bdrv_unmap resulted in a call to continue_after_map_failure,
the bottom half would be cancelled immediately. So we changed from:
dbs->in_cancel = false;
/* dma_complete calls dma_bdrv_unmap */
for (i = 0; i < dbs->iov.niov; ++i) {
/* might schedule dbs->bh */
dma_memory_unmap(dbs->sg->as, dbs->iov.iov[i].iov_base,
dbs->iov.iov[i].iov_len, dbs->dir,
dbs->iov.iov[i].iov_len);
}
qemu_iovec_reset(&dbs->iov);
/* back to dma_complete, dbs->common.cb == NULL */
qemu_iovec_destroy(&dbs->iov);
if (dbs->bh) {
/* dbs->bh now unscheduled, so it will never run */
qemu_bh_delete(dbs->bh);
dbs->bh = NULL;
}
/* dbs->in_cancel is false here. */
if (!dbs->in_cancel) {
/* Requests may complete while dma_aio_cancel is in progress.
* this case, the AIOCB should not be released because it is
* still referenced by dma_aio_cancel. */
qemu_aio_release(dbs);
}
to
dbs->in_cancel = false;
/* dma_complete calls dma_bdrv_unmap */
for (i = 0; i < dbs->iov.niov; ++i) {
/* might schedule dbs->bh */
dma_memory_unmap(dbs->sg->as, dbs->iov.iov[i].iov_base,
dbs->iov.iov[i].iov_len, dbs->dir,
dbs->iov.iov[i].iov_len);
}
qemu_iovec_reset(&dbs->iov);
/* back to dma_complete, dbs->common.cb == NULL */
qemu_iovec_destroy(&dbs->iov);
if (dbs->bh) {
/* dbs->bh now unscheduled, so it will never run */
qemu_bh_delete(dbs->bh);
dbs->bh = NULL;
}
/* after the patch dbs->in_cancel is true, the if never triggers */
if (!dbs->in_cancel) {
/* Requests may complete while dma_aio_cancel is in progress.
* this case, the AIOCB should not be released because it is
* still referenced by dma_aio_cancel. */
qemu_aio_release(dbs);
}
/* back to dma_aio_cancel */
qemu_aio_release(dbs);
This doesn't make sense to me. Can you find out where I'm wrong?
Paolo
