After updating to v5.9, I've started seeing errors in the kernel log when using device tree overlays. Specifically, the problem seems to happen when removing a device tree overlay that contains two devices with some dependency between them (e.g., a device that provides a clock and a device that consumes that clock). Removing such an overlay results in: OF: ERROR: memory leak, expected refcount 1 instead of 2, of_node_get()/of_node_put() unbalanced - destroy OF: ERROR: memory leak, expected refcount 1 instead of 2, of_node_get()/of_node_put() unbalanced - destroy followed by hitting some REFCOUNT_WARNs in refcount.c In the first patch, I've included a unittest that can be used to reproduce this when built with CONFIG_OF_UNITTEST [1]. I believe the issue is caused by the cleanup performed when releasing the devlink device that's created to represent the dependency between devices. The devlink device has references to the consumer and supplier devices, which it drops in device_link_free; the devlink device's release callback calls device_link_free via call_srcu. When the overlay is being removed, all devices are removed, and eventually the release callback for the devlink device run, and schedules cleanup using call_srcu. Before device_link_free can and call put_device on the consumer/supplier, the rest of the overlay removal process runs, resulting in the error traces above. Patches 2 and 3 are an attempt at fixing this: call srcu_barrier to wait for any pending device_link_free's to execute before continuing on with the removal process. These patches resolve the issue, but probably not in the best way. In particular, it seems strange to need to leak details of devlinks into the device tree overlay code. So, I'd be curious to get some feedback or hear any other ideas for how to resolve this issue. Thanks, Michael 1. Note that this isn't a very good unit test: it will report a "pass" even if it fails with the aforementioned errors, as these errors aren't propogated. Michael Auchter (3): of: unittest: add test of overlay with devlinks driver core: add device_links_barrier of: dynamic: add device links barrier before detach drivers/base/core.c | 10 ++++++++++ drivers/of/dynamic.c | 3 +++ drivers/of/unittest-data/Makefile | 1 + drivers/of/unittest-data/overlay_16.dts | 26 +++++++++++++++++++++++++ drivers/of/unittest.c | 16 +++++++++++++++ include/linux/device.h | 1 + 6 files changed, 57 insertions(+) create mode 100644 drivers/of/unittest-data/overlay_16.dts -- 2.25.4
