Re: [PATCH v5 00/13] exit_net checks for objects initialized in net_init hook

From: Vasily Averin <redacted>
Date: Sun, 12 Nov 2017 22:26:44 +0300

OpenVz kernel team have a long history of fighting against namespace-related bugs,
some of them could be prevented by using simple checks described below.

One of typical errors is related to live cycle of namespaces:
usually objects created for some namespace should not live longer than namespace itself.

Such kind of issues can be invisible on usual systems where additional namespaces
are not used, because initial namespaces usually lives forever and never destroyed.

However in systems with namespaces it can lead to memory leaks or to use-after-free.
Both of them are critical for systems with running containers.
As you knows it's quite hard to find the reason of such issues,
especially in rarely-triggered scenarios on production nodes on default kernels
without specially enabled debug settings. Any additional hints can be useful here.

This patch set should help to detect some of these issues.
It is based on assumption that objects initialized in init hook of pernet_operations
should return to initial state until end of exit hook.

Many drivers and subsystems already have such checks, however I've found number
of places where list_empty check would be useful at least as smoke test.

These checks are useful for long-term stable kernels,
they allows to detect problems related to incomplete or incorrectly
backported patches.

All applied to net-next except patch #9 and #10 which need to go via the
NFS maintainer.