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Re: [qemu-s390x] [PATCH v3 1/6] vfio-ccw: make it safe to access channel

From: Cornelia Huck
Subject: Re: [qemu-s390x] [PATCH v3 1/6] vfio-ccw: make it safe to access channel programs
Date: Thu, 31 Jan 2019 12:52:20 +0100

On Wed, 30 Jan 2019 19:51:27 +0100
Halil Pasic <address@hidden> wrote:

> On Wed, 30 Jan 2019 14:22:07 +0100
> Cornelia Huck <address@hidden> wrote:
> > When we get a solicited interrupt, the start function may have
> > been cleared by a csch, but we still have a channel program
> > structure allocated. Make it safe to call the cp accessors in
> > any case, so we can call them unconditionally.  
> I read this like it is supposed to be safe regardless of
> parallelism and threads. However I don't see any explicit
> synchronization done for cp->initialized.
> I've managed to figure out how is that supposed to be safe
> for the cp_free() (which is probably our main concern) in
> vfio_ccw_sch_io_todo(), but if fail when it comes to the one
> in vfio_ccw_mdev_notifier().
> Can you explain us how does the synchronization work?

You read that wrong, I don't add synchronization, I just add a check.

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