Re: [PATCH] cpufreq: amd-pstate: fix global sysfs attribute type

[Nathan Chancellor <nathan@kernel.org>]

Hi Thomas,

On Mon, Aug 07, 2023 at 08:37:45AM +0200, Thomas Weißschuh wrote:
> In commit 3666062b87ec ("cpufreq: amd-pstate: move to use bus_get_dev_root()")
> the "amd_pstate" attributes where moved from a dedicated kobject to the
> cpu root kobject.
> While the dedicated kobject expects to contain kobj_attributes the root
> kobject needs device_attributes.
> 
> As the changed arguments are not used by the callbacks it works most of
> the time.
> However CFI will detect this issue:
> 
> [ 4947.849350] CFI failure at dev_attr_show+0x24/0x60 (target: show_status+0x0/0x70; expected type: 0x8651b1de)
> ...
> [ 4947.849409] Call Trace:
> [ 4947.849410]  <TASK>
> [ 4947.849411]  ? __warn+0xcf/0x1c0
> [ 4947.849414]  ? dev_attr_show+0x24/0x60
> [ 4947.849415]  ? report_cfi_failure+0x4e/0x60
> [ 4947.849417]  ? handle_cfi_failure+0x14c/0x1d0
> [ 4947.849419]  ? __cfi_show_status+0x10/0x10
> [ 4947.849420]  ? handle_bug+0x4f/0x90
> [ 4947.849421]  ? exc_invalid_op+0x1a/0x60
> [ 4947.849422]  ? asm_exc_invalid_op+0x1a/0x20
> [ 4947.849424]  ? __cfi_show_status+0x10/0x10
> [ 4947.849425]  ? dev_attr_show+0x24/0x60
> [ 4947.849426]  sysfs_kf_seq_show+0xa6/0x110
> [ 4947.849433]  seq_read_iter+0x16c/0x4b0
> [ 4947.849436]  vfs_read+0x272/0x2d0
> [ 4947.849438]  ksys_read+0x72/0xe0
> [ 4947.849439]  do_syscall_64+0x76/0xb0
> [ 4947.849440]  ? do_user_addr_fault+0x252/0x650
> [ 4947.849442]  ? exc_page_fault+0x7a/0x1b0
> [ 4947.849443]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> 
> Reported-by: Jannik Glückert <jannik.glueckert@gmail.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217765
> Link: https://lore.kernel.org/lkml/c7f1bf9b-b183-bf6e-1cbb-d43f72494083@gmail.com/
> Fixes: 3666062b87ec ("cpufreq: amd-pstate: move to use bus_get_dev_root()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Thanks a lot for the quick patch! Unfortunately, it seems like neither
of my AMD machines support amd-pstate so I can't test this but it seems
like the right fix to me.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
> Note:
> 
> This was not tested with CFI as I don't have the toolchain available.

For the record, I have LLVM toolchains on kernel.org that should be
relatively standalone enough to have them somewhere on your hard drive
then use the LLVM=<prefix>/bin/ syntax that has been supported since
5.18:

https://mirrors.edge.kernel.org/pub/tools/llvm/

> Jannik, could you give it a spin?
> ---
>  drivers/cpufreq/amd-pstate.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 81fba0dcbee9..9a1e194d5cf8 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1012,8 +1012,8 @@ static int amd_pstate_update_status(const char *buf, size_t size)
>  	return 0;
>  }
>  
> -static ssize_t show_status(struct kobject *kobj,
> -			   struct kobj_attribute *attr, char *buf)
> +static ssize_t status_show(struct device *dev,
> +			   struct device_attribute *attr, char *buf)
>  {
>  	ssize_t ret;
>  
> @@ -1024,7 +1024,7 @@ static ssize_t show_status(struct kobject *kobj,
>  	return ret;
>  }
>  
> -static ssize_t store_status(struct kobject *a, struct kobj_attribute *b,
> +static ssize_t status_store(struct device *a, struct device_attribute *b,
>  			    const char *buf, size_t count)
>  {
>  	char *p = memchr(buf, '\n', count);
> @@ -1043,7 +1043,7 @@ cpufreq_freq_attr_ro(amd_pstate_lowest_nonlinear_freq);
>  cpufreq_freq_attr_ro(amd_pstate_highest_perf);
>  cpufreq_freq_attr_rw(energy_performance_preference);
>  cpufreq_freq_attr_ro(energy_performance_available_preferences);
> -define_one_global_rw(status);
> +static DEVICE_ATTR_RW(status);
>  
>  static struct freq_attr *amd_pstate_attr[] = {
>  	&amd_pstate_max_freq,
> @@ -1062,7 +1062,7 @@ static struct freq_attr *amd_pstate_epp_attr[] = {
>  };
>  
>  static struct attribute *pstate_global_attributes[] = {
> -	&status.attr,
> +	&dev_attr_status.attr,
>  	NULL
>  };
>  
> 
> ---
> base-commit: 52a93d39b17dc7eb98b6aa3edb93943248e03b2f
> change-id: 20230807-amd-pstate-cfi-8302498c54f5
> 
> Best regards,
> -- 
> Thomas Weißschuh <linux@weissschuh.net>
>