[libvirt PATCH] Fix incorrect uses of g_clear_pointer() introduced in 8.1.0

[Ján Tomko]

On a Sunday in 2022, Mark Mielke wrote:
>This is a partial revert of 87a43a907f0ad4897a28ad7c216bc70f37270b93.

I'll drop the trailing period before pushing.

>
>The change to use g_clear_pointer() in more places was accidentally
>applied to cases involving vir_g_source_unref().
>
>In some cases, the ordering of g_source_destroy() and
>vir_g_source_unref() was reversed, which resulted in the source being
>marked as destroyed, after it is already unreferenced.

Oops, sorry I missed that during review.

>This
>use-after-free case might work in many cases, but with versions of
>glibc older than 2.64.0 it may defer unref to run within the main

s/glibc/glib/

>thread to avoid a race condition, which creates a large distance
>between the g_source_unref() and g_source_destroy().
>
>In some cases, the call to vir_g_source_unref() was replaced with a
>second call to g_source_destroy(), leading to a memory leak or worse.
>
>In our experience, the symptoms were that use of libvirt-python became
>slower over time, with OpenStack nova-compute initially taking around
>one second to periodically query the host PCI devices, and within an
>hour it was taking over a minute to complete the same operation, until
>it is was eventually running this query back-to-back, resulting in the
>nova-compute process consuming 100% of one CPU thread, losing its
>RabbitMQ connection frequently, and showing up as down to the control
>plane.

Your patch is missing a sign-off
https://libvirt.org/hacking.html#developer-certificate-of-origin

Just replying to this e-mail with the Signed-off-by line is enough - no
need to resend the patch. I'll push it with the sign-off included after
the pipeline succeds: https://gitlab.com/janotomko/libvirt/-/pipelines/562139546

>---
> src/qemu/qemu_agent.c   |  3 ++-
> src/qemu/qemu_monitor.c |  3 ++-
> src/util/vireventglib.c | 12 ++++++++----
> 3 files changed, 12 insertions(+), 6 deletions(-)
>

Reviewed-by: Ján Tomko <jtomko at redhat.com>

Jano
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