Re: [PATCH 2/2] virtio: Drop out of coroutine context in virtio_load()

[Kevin Wolf <kwolf@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 1013 bytes --]

Am 07.09.2023 um 20:40 hat Stefan Hajnoczi geschrieben:
> On Tue, Sep 05, 2023 at 04:50:02PM +0200, Kevin Wolf wrote:
> > virtio_load() as a whole should run in coroutine context because it
> > reads from the migration stream and we don't want this to block.
> 
> Is that "should" a "must" or a "can"?
> 
> If it's a "must" then virtio_load() needs assert(qemu_in_coroutine()).
> 
> But the previous patch mentioned that loadvm for snapshots calls it
> outside coroutine context. So maybe it's a "can"?

Where this makes a difference is when the function indirectly calls into
QIOChannel. When called from a coroutine, it yields while waiting for
I/O, and outside of a coroutine it blocks. Yielding is always
preferable, but in cases like HMP savevm/loadvm we also don't really
care because it's synchronous anyway.

Whether that makes it a MAY or a SHOULD in the RFC sense, you decide.
If you wanted to make it a MUST, you'd need to check all callers first
and change some of them.

Kevin

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]