linux-kernel - Re: [PATCH] proc/wchan: Use printk format instead of lookup_symbol

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Date:   Wed, 23 Dec 2020 10:48:10 +0100
From:   Helge Deller <deller@....de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] proc/wchan: Use printk format instead of
 lookup_symbol_name()

On 12/23/20 3:18 AM, Andrew Morton wrote:
> On Thu, 17 Dec 2020 17:54:13 +0100 Helge Deller <deller@....de> wrote:
>
>> To resolve the symbol fuction name for wchan, use the printk format
>> specifier %ps instead of manually looking up the symbol function name
>> via lookup_symbol_name().
>>
>> Signed-off-by: Helge Deller <deller@....de>
>>
>
> Please don't forget the "^---$" to separate the changelog from the
> diff.

Ok.

>
>>  #include <linux/module.h>
>> @@ -386,19 +385,17 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
>>  			  struct pid *pid, struct task_struct *task)
>>  {
>>  	unsigned long wchan;
>> -	char symname[KSYM_NAME_LEN];
>>
>> -	if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
>> -		goto print0;
>> +	if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
>> +		wchan = get_wchan(task);
>> +	else
>> +		wchan = 0;
>>
>> -	wchan = get_wchan(task);
>> -	if (wchan && !lookup_symbol_name(wchan, symname)) {
>> -		seq_puts(m, symname);
>> -		return 0;
>> -	}
>> +	if (wchan)
>> +		seq_printf(m, "%ps", (void *) wchan);
>> +	else
>> +		seq_putc(m, '0');
>>
>> -print0:
>> -	seq_putc(m, '0');
>>  	return 0;
>>  }
>
> We can simplify this further?
>
> static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
> 			  struct pid *pid, struct task_struct *task)
> {
> 	if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
> 		seq_printf(m, "%ps", (void *)get_wchan(task));
> 	else
> 		seq_putc(m, '0');
>
> 	return 0;
> }
>
>
> --- a/fs/proc/base.c~proc-wchan-use-printk-format-instead-of-lookup_symbol_name-fix
> +++ a/fs/proc/base.c
> @@ -384,15 +384,8 @@ static const struct file_operations proc
>  static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
>  			  struct pid *pid, struct task_struct *task)
>  {
> -	unsigned long wchan;
> -
>  	if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
> -		wchan = get_wchan(task);
> -	else
> -		wchan = 0;
> -
> -	if (wchan)
> -		seq_printf(m, "%ps", (void *) wchan);
> +		seq_printf(m, "%ps", (void *)get_wchan(task));
>  	else
>  		seq_putc(m, '0');

get_wchan() does return NULL sometimes, in which case with
your change now "0x0" instead of "0" gets printed.

If that's acceptable, then your patch is Ok.

Helge