On Wed, Apr 19, 2017 at 2:46 AM, Rob Herring [off-list ref] wrote:

On Mon, Apr 17, 2017 at 7:32 PM, Tyrel Datwyler
[off-list ref] wrote:

quoted

This patch introduces event tracepoints for tracking a device_nodes
reference cycle as well as reconfig notifications generated in response
to node/property manipulations.

With the recent upstreaming of the refcount API several device_node
underflows and leaks have come to my attention in the pseries (DLPAR) dynamic
logical partitioning code (ie. POWER speak for hotplugging virtual and physcial
resources at runtime such as cpus or IOAs). These tracepoints provide a
easy and quick mechanism for validating the reference counting of
device_nodes during their lifetime.

Not really relevant for this patch, but since you are looking at
pseries and refcounting, the refcounting largely exists for pseries.
It's also hard to get right as this type of fix is fairly common. It's
now used for overlays, but we really probably only need to refcount
the overlays or changesets as a whole, not at a node level. If you
have any thoughts on how a different model of refcounting could work
for pseries, I'd like to discuss it.

One idea I've been kicking around is differentiating short and long
term references to a node. I figure most leaks are due to a missing
of_node_put() within a stack frame so it might be possible to use the
ftrace infrastructure to detect and emit warnings if a short term
reference is leaked. Long term references are slightly harder to deal
with, but they're less common so we can add more detailed reference
tracking there (devm_of_get_node?).

Oliver