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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <1c4ee8ba-c179-0a8c-0fe3-ffa1be38e0a5@redhat.com>
Date: Wed, 23 Aug 2017 18:15:35 +0200
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Subject: Re: [Qemu-devel] [PATCH] nbd-client: avoid spurious
 qio_channel_yield() re-entry
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: qemu-devel@nongnu.org, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, qemu-block@nongnu.org, Eric Blake <eblake@redhat.com>

On 23/08/2017 16:45, Stefan Hajnoczi wrote:
> That depends on the BDRV_POLL_WHILE() allowing all request coroutines to
> terminate before we call nbd_client_detach_aio_context():
> 
>     qio_channel_shutdown(client->ioc,
>                          QIO_CHANNEL_SHUTDOWN_BOTH,
>                          NULL);
>     BDRV_POLL_WHILE(bs, client->read_reply_co);
> 
>     nbd_client_detach_aio_context(bs);
> 
> I'm not sure we have any guarantee that request coroutines will have
> terminated.

Ok, I see my confusion, it's only because of the "receiving" flag which
actually means "waiting for reply".  Your patch is okay.

Paolo

> Once nbd_client_detach_aio_context() is called
> ioc->read_coroutine/write_coroutine are set to NULL.  At that point any
> remaining coroutine doing I/O on ioc will be in trouble.