linux-kernel - Re: [PATCH v17 1/3] proc: add /proc/<pid>/arch

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Date:   Thu, 25 Apr 2019 09:50:46 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     mingo@...hat.com, peterz@...radead.org, hpa@...or.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        dave.hansen@...el.com, arjan@...ux.intel.com, adobriyan@...il.com,
        akpm@...ux-foundation.org, aubrey.li@...el.com,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v17 1/3] proc: add /proc/<pid>/arch_status

On 2019/4/25 5:18, Thomas Gleixner wrote:
> On Mon, 22 Apr 2019, Aubrey Li wrote:
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 5ad92419be19..d5a9c5ddd453 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -208,6 +208,7 @@ config X86
>>  	select USER_STACKTRACE_SUPPORT
>>  	select VIRT_TO_BUS
>>  	select X86_FEATURE_NAMES		if PROC_FS
>> +	select PROC_PID_ARCH_STATUS		if PROC_FS
> 
> Can you please stop mixing arch and proc code? There is no point in
> enabling this on x86 right away.
> 
>> +
>> +config PROC_PID_ARCH_STATUS
>> +	bool "Enable /proc/<pid>/arch_status file"
> 
> Why is this switchable? x86 selects it if PROC_FS is enabled and all other
> architectures are absolutely not interested in this.

Above and this, I was trying to avoid an empty arch_file on other architectures.
In previous proposal the entry only exists on the platform with AVX512.

> 
>> +	default n
>> +	help
>> +	  Provides a way to examine process architecture specific information.
>> +	  See <file:Documentation/filesystems/proc.txt> for more information.
> 
> Which contains zero information about this file when only this patch is
> applied. 
> 
>> @@ -94,6 +94,7 @@
>>  #include <linux/sched/debug.h>
>>  #include <linux/sched/stat.h>
>>  #include <linux/posix-timers.h>
>> +#include <linux/processor.h>
> 
> That include is required because it does NOT contain anything useful for
> this, right?
> 
>> +/*
>> + * Add support for task architecture specific output in /proc/pid/arch_status.
>> + * task_arch_status() must be defined in asm/processor.h
>> + */
>> +#ifdef CONFIG_PROC_PID_ARCH_STATUS
>> +# ifndef task_arch_status
>> +# define task_arch_status(m, task)
>> +# endif
> 
> What exactly is the point of this macro mess? If an architecture selects
> CONFIG_PROC_PID_ARCH_STATUS then it has to provide proc_task_arch_status()
> and the prototype should be in include/linux/proc_fs.h.

I was trying to address Andy's last comments. If we have the prototype in 
include/linux/proc_fs.h, we'll have a weak function definition in fs/proc/array.c,
which bloats other architectures.

In that way proc_task_arch_status() should be defined in asm/processor.h,
but proc_task_arch_status() has four parameters, I don't want unnecessary
"struct pid_namespace *ns" and "struct pid *pid" leaked into arch headers,
so I defined task_arch_status(m, task) to avoid that.

> 
>> +static int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
>> +				struct pid *pid, struct task_struct *task)
>> +{
>> +	task_arch_status(m, task);
>> +	return 0;
>> +}
>> +#endif /* CONFIG_PROC_PID_ARCH_STATUS */
> 
> Thanks,
> 
> 	tglx
> 

Thanks,
-Aubrey