Re: [Qemu-devel] [PATCH for-2.12 v2] iothread: workaround glib bug which hangs qmp-test

[Eric Blake <eblake@redhat.com>]

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On 04/09/2018 03:39 AM, Peter Xu wrote:
> Free the AIO context earlier than the GMainContext (if we have) to
> workaround a glib2 bug that GSource context pointer is not cleared even
> if the context has already been destroyed (while it should).
> 
> The patch itself only changed the order to destroy the objects, no
> functional change at all. Without this workaround, we can encounter
> qmp-test hang with oob (and possibly any other use case when iothread is
> used with GMainContexts):
> 

> The glib2 bug is fixed in commit 26056558b ("gmain: allow
> g_source_get_context() on destroyed sources", 2012-07-30), the first
> good version is glib2 2.33.10. So this error will be encountered before
> any glib version older than 2.33.10 (not including). Since we are still
> supporting even older glib versions, we may want this workaround.

Grammar is awkward; I'd suggest:

...the first good version is glib2 2.33.10.  But we still support
building with glib as old as 2.28, so we need the workaround.

> 
> Let's make sure we destroy the GSources first before its owner context
> until we drop support for glibs older than 2.33.10.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> v2:
> - verified the root cause of the bug, and enhance commit message and
>   comments correspondingly

Reviewed-by: Eric Blake <eblake@redhat.com>

If Stefan is happy with your improved commit message, I'll queue this
for -rc3.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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