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

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Message-Id: <20201222181807.360cd9458d50b625608b8b44@linux-foundation.org>
Date:   Tue, 22 Dec 2020 18:18:07 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Helge Deller <deller@....de>
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 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.

>  #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');
 
_