[PATCH v2 0/7] nvmem: survive unbind with active consumers

[Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>]

Nvmem is one of the subsystems vulnerable to object life-time issues.
The memory nvmem core dereferences is owned by nvmem providers which can
be unbound at any time and even though nvmem devices themselves are
reference-counted, there's no synchronization with the provider modules.

This typically is not a problem because thanks to fw_devlink, consumers
get synchronously unbound before providers but it's enough to pass
fw_devlink=off over the command line, unbind the nvmem controller with
consumers still holding references to it and try to read/write in order
to see fireworks in the kernel log.

User-space can trigger it too if a device (for instance: i2c eeprom on a
cp2112 USB expander) is unplugged halfway through a long read.

Thankfully the design of nvmem is rather sane so it just needs a bit of
encouragement and synchronization.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
Changes in v2:
- add missing SRCU struct cleanup
- improve the teardown path on error in nvmem_register()
- Link to v1: https://lore.kernel.org/r/20260116-nvmem-unbind-v1-0-7bb401ab19a8@oss.qualcomm.com

---
Bartosz Golaszewski (7):
      nvmem: remove unused field from struct nvmem_device
      nvmem: return -EOPNOTSUPP to in-kernel users on missing callbacks
      nvmem: check the return value of gpiod_set_value_cansleep()
      nvmem: simplify locking with guard()
      nvmem: remove unneeded __nvmem_device_put()
      nvmem: split struct nvmem_device into refcounted and provider-owned data
      nvmem: synchronize nvmem device unregistering with SRCU

 drivers/nvmem/core.c      | 295 +++++++++++++++++++++++++---------------------
 drivers/nvmem/internals.h |  18 ++-
 2 files changed, 173 insertions(+), 140 deletions(-)
---
base-commit: d75756d8d78aa50d454b92665896b3cd0d1077bb
change-id: 20260114-nvmem-unbind-673b52fc84a0

Best regards,
-- 
Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>