From: Paolo Bonzini <pbonzini@redhat.com>
To: John Snow <jsnow@redhat.com>, qemu-devel@nongnu.org
Cc: Qemu-block <qemu-block@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH] dma-helpers: ensure AIO callback is invoked after cancellation
Date: Mon, 29 Jul 2019 23:51:48 +0200 [thread overview]
Message-ID: <8993ddbe-0a2f-feb0-9d1c-cbb5ea83bbc5@redhat.com> (raw)
In-Reply-To: <e8d53076-f5d0-ed13-110b-0cce911a07ec@redhat.com>
On 29/07/19 23:46, John Snow wrote:
>> @@ -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;
>> - }
>
> Now presumably handled by dma_aio_cancel,
No, it simply could never happen. dma_complete is called here in dma_blk_cb:
dbs->acb = NULL;
dbs->offset += dbs->iov.size;
if (dbs->sg_cur_index == dbs->sg->nsg || ret < 0) {
dma_complete(dbs, ret);
return;
}
and the only way to reach that when dbs->bh becomes non-NULL is through
reschedule_dma, which clears dbs->bh before invoking dma_blk_cb.
>> if (dbs->acb) {
>> + /* This will invoke dma_blk_cb. */
>
> uhh, does it?
Yes:
/* Async version of aio cancel. The caller is not blocked if the acb implements
* cancel_async, otherwise we do nothing and let the request normally complete.
* In either case the completion callback must be called. */
> this is maybe where I got lost reading this code.
> Isn't dbs->acb going to be what was returned from e.g.
> dma_blk_read_io_func, which ultimately uses blk_aio_em_aiocb_info, that
> has no cancel callback?
Right therefore the I/O will complete and the callback will be invoked.
> Well, here at least I am now on terra-firma that we're going to call the
> original callback with ECANCELED, which is a step towards code that
> isn't surprising my sensibilities.
Good. :)
Paolo
next prev parent reply other threads:[~2019-07-29 21:52 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 21:34 [Qemu-devel] [PATCH] dma-helpers: ensure AIO callback is invoked after cancellation Paolo Bonzini
2019-07-29 21:46 ` John Snow
2019-07-29 21:51 ` Paolo Bonzini [this message]
2019-07-29 22:00 ` John Snow
2019-08-13 22:40 ` John Snow
2019-08-13 22:49 ` John Snow
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