Re: [PATCH v4 0/4] devfreq: Add refcounts for governor modules

["zhenglifeng (A)" <zhenglifeng1@huawei.com>]

On 7/29/2026 6:23 PM, Jie Zhan wrote:
> A governor module can be dynamically inserted or removed if compiled as a
> kernel module.  'devfreq->governor' would become NULL if the governor
> module is removed when it's in use.
> 
> For user-friendliness, get and put the module refcount of a governor module
> when it's in use.  As a result, unloading a governor module in use returns
> an error, e.g.:
> 
> $ cat governor
> performance
> $ rmmod governor_performance
> rmmod: ERROR: Module governor_performance is in use
> 
> Note that this can't stop force unload, so it's more of a
> user-friendliness improvement rather than strict protection.  The
> existing code that keeps devfreq working when 'devfreq->governor' is
> NULL should still be there.
> 
> Patch 1-3 clean up mutex with guards and factor out a common governor
> setting function, so as to prepare for implementing governor reference
> counting.  They can be applied separately.
> 
> Patch 4 adds the reference counting mechanism for devfreq governor
> modules.
> 
> This set is based on devfreq-next of 7.1-rc1.
> 
> Changelog
> ---------
> v4:
> - Patch 3: Return an error if starting new governor fails and restoring
>   old governor succeeds, such that the caller won't get misled.
> 
> v3:
> - Link: https://lore.kernel.org/all/20260519113251.3745140-1-zhanjie9@hisilicon.com/
> - Rework patch 4 to make the 'owner' field assignment optional in the
>   governor code.  This prevents device-driver-bundled governors (such as
>   those in hisi_uncore_freq and tegra30-devfreq) from causing
>   self-reference issues that block module removal. Additionally, merge
>   patches 4 and 5 to clearly present the new 'owner' member alongside
>   its usage.
> - Drop patch 6 because it's no longer needed since v2.
> - Update commit logs of patch 3 and 4 to clarify background and
>   motivation.
> - Pick up 2 tags from Yaxiong (thanks!).
> - Trivial cleanups.
> 
> v2:
> - Link: https://lore.kernel.org/all/20260513093832.1645890-1-zhanjie9@hisilicon.com/
> - Rebase on devfreq-next of 7.1-rc1.
> - Drop the patches related to the NULL pointer deference issue of
>   'devfreq->governor', which has been solved and merged recently.
> - Remove the dedicated mutex for 'devfreq_governor_list' because the
>   refcount changes don't depend on that.
> - Some minor cleanups and fixes.
> 
> v1:
> - Link: https://lore.kernel.org/all/20260326123428.800407-1-zhanjie9@hisilicon.com/
> 
> Jie Zhan (4):
>   devfreq: Use mutex guard in governor_store()
>   devfreq: Use mutex guard in devfreq_add/remove_governor()
>   devfreq: Factor out devfreq_set_governor()
>   devfreq: Refcount governor modules while in use
> 
>  drivers/devfreq/devfreq.c                 | 185 +++++++++++-----------
>  drivers/devfreq/governor_passive.c        |   1 +
>  drivers/devfreq/governor_performance.c    |   1 +
>  drivers/devfreq/governor_powersave.c      |   1 +
>  drivers/devfreq/governor_simpleondemand.c |   1 +
>  drivers/devfreq/governor_userspace.c      |   1 +
>  include/linux/devfreq-governor.h          |  11 ++
>  7 files changed, 112 insertions(+), 89 deletions(-)
> 

LGTM.

Reviewed-by: Lifeng Zheng <zhenglifeng1@huawei.com>