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Date:   Mon, 28 Dec 2020 21:28:38 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     akpm@linux-foundation.org
Cc:     linux-kernel@vger.kernel.org, deller@gmx.de
Subject: Re: +
 proc-wchan-use-printk-format-instead-of-lookup_symbol_name-fix.patch added
 to -mm tree
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References: <20201223021834.9n93L%akpm@linux-foundation.org>
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On Tue, Dec 22, 2020 at 06:18:34PM -0800, akpm@linux-foundation.org wrote:
>
>      proc-wchan-use-printk-format-instead-of-lookup_symbol_name-fix.patch

> --- 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');

These patches change '0' to '0x0'.

Also /proc/*/wchan shows '0' for everything which is strange.

I'm not sure if we should care as wchan is obsoleted by /proc/*/stack .