Re: [PATCH v2 1/4] PM / devfreq: Fix possible null pointer issue in devfreq_add_governor()

[Jie Zhan <zhanjie9@hisilicon.com>]

On 4/1/2026 11:30 AM, Yaxiong Tian wrote:
> When a user removes a governor using devfreq_remove_governor(), if
> the current device is using this governor, devfreq->governor will
> be set to NULL. When the user registers any governor
> using devfreq_add_governor(), since devfreq->governor is NULL, a
> null pointer error occurs in strncmp().
> 
> For example: A user loads the userspace gov through a module, then
> a device selects userspace. When unloading the userspace module and
> then loading it again, the null pointer error occurs:
> 
> Unable to handle kernel NULL pointer dereference at virtual address
> 0000000000000010
> Mem abort info:
> ESR = 0x0000000096000004
> EC = 0x25: DABT (current EL), IL = 32 bits
> *******************skip *********************
> Call trace:
> __pi_strncmp+0x20/0x1b8
> devfreq_userspace_init+0x1c/0xff8 [governor_userspace]
> do_one_initcall+0x4c/0x278
> do_init_module+0x5c/0x218
> load_module+0x1f1c/0x1fc8
> init_module_from_file+0x8c/0xd0
> __arm64_sys_finit_module+0x220/0x3d8
> invoke_syscall+0x48/0x110
> el0_svc_common.constprop.0+0xbc/0xe8
> do_el0_svc+0x20/0x30
> el0_svc+0x24/0xb8
> el0t_64_sync_handler+0xb8/0xc0
> el0t_64_sync+0x14c/0x150
> 
> To fix this issue, remove the list_for_each_entry() logic, as
> find_devfreq_governor() has already checked for the existence of
> governor with the same name. This makes it impossible to find a
> duplicate governor in the list, so the subsequent logic is
> unreachable and can be removed.
> 
> Fixes: 1b5c1be2c88e ("PM / devfreq: map devfreq drivers to governor using name")
> Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
> ---
>  drivers/devfreq/devfreq.c | 33 ---------------------------------
>  1 file changed, 33 deletions(-)
> 
> Hi Jie Zhan: 
> 	If you're willing, I'd like to add your Co-developed-by tag.
Yeah please do so.  That would be:
Co-developed-by: Jie Zhan <zhanjie9@hisilicon.com>
Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>

The rest looks good to me.