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Re: [Qemu-devel] [PATCH 07/12] nbd: Increase bs->in_flight during AioCon
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 07/12] nbd: Increase bs->in_flight during AioContext switch |
Date: |
Mon, 18 Feb 2019 18:22:59 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 |
On 18/02/19 17:18, Kevin Wolf wrote:
> + /* aio_ctx_switch is only supposed to be set if we're sitting in
> + * the qio_channel_yield() below. */
> + assert(!*aio_ctx_switch);
> bdrv_dec_in_flight(bs);
> qio_channel_yield(ioc, G_IO_IN);
> - bdrv_inc_in_flight(bs);
> + if (*aio_ctx_switch) {
> + /* nbd_client_attach_aio_context() already increased
> in_flight
> + * when scheduling this coroutine for reentry */
> + *aio_ctx_switch = false;
> + } else {
> + bdrv_inc_in_flight(bs);
> + }
Hmm, my first thought would have been to do the bdrv_inc_in_flight(bs);
unconditionally here, and in nbd_connection_entry do the opposite, like
if (s->aio_ctx_switch) {
s->aio_ctx_switch = false;
bdrv_dec_in_flight(bs);
}
but I guess the problem is that then bdrv_drain could hang.
So my question is:
1) is there a testcase that shows the problem with this "obvious"
refactoring;
2) maybe instead of aio_co_schedul-ing client->connection_co and having
the s->aio_ctx_switch flag, you could go through a bottom half that does
the bdrv_inc_in_flight and then enters client->connection_co?
Paolo
- [Qemu-devel] [PATCH 00/12] block: bdrv_set_aio_context() related fixes, Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 01/12] block-backend: Make blk_inc/dec_in_flight public, Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 08/12] block: Don't poll in bdrv_set_aio_context(), Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 02/12] virtio-blk: Increase in_flight for request restart BH, Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 10/12] test-bdrv-drain: AioContext switch in drained section, Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 07/12] nbd: Increase bs->in_flight during AioContext switch, Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 09/12] block: Fix AioContext switch for drained node, Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 03/12] nbd: Restrict connection_co reentrance, Kevin Wolf, 2019/02/18
- [Qemu-devel] [PATCH 11/12] block: Use normal drain for bdrv_set_aio_context(), Kevin Wolf, 2019/02/18