Re: [Qemu-devel] [PATCH 0/4] RFC: make chardev context switching safer

[Peter Xu <peterx@redhat.com>]

On Wed, Feb 20, 2019 at 05:06:24PM +0100, Marc-André Lureau wrote:
> Hi,

Hi,

> 
> The chardev context switching code is a bit fragile, as it works as if
> the current context is properly synchronized with the new context.  It
> isn't so obvious to me that concurrent usage of chardev can't happen,
> as there might be various main loop sources being dispatched during
> the switch.
> 
> Worried about the situation, I wrote those patches a while ago, I
> think they are still worth to consider. I used to have some basic
> test, but it now conflicts a lot with recent changes. I would like to
> get some feedback about the series before I rewrite it.
> 
> The importat patch is "chardev: make qemu_chr_fe_set_handlers()
> context switching safer". It works by "freezing" the given contexts
> while the chardev will "move" (recreate to the new context) the
> various sources it owns. This looks quite ugly to me overall, but still
> safer than today.
> 
> This should allow to simplify the scary code from "monitor: set the
> chardev context from the main context/thread".

Indeed it's at least not that friendly to readers... so out of
curiosity - is this the only reason for this series?

> 
> Finally, "char-socket: restart the reconnect timer to switch context"
> shows that we have chardev backends that do not switch fully yet.

This seems irrelevant to the series, or am I wrong?

Thanks,

-- 
Peter Xu