linux-kernel - Re: [PATCH] fs/proc: add Kthread flag to /proc/$pid/status

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Date:   Sat, 15 Apr 2023 09:03:17 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Chunguang Wu <fullspring2018@...il.com>, akpm@...ux-foundation.org,
        corbet@....net
Cc:     adobriyan@...il.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] fs/proc: add Kthread flag to /proc/$pid/status

Hi,

On 4/15/23 01:21, Chunguang Wu wrote:
> The command `ps -ef ` and `top -c` mark kernel thread by '['
> and ']', but sometimes the result is not correct.
> The task->flags in /proc/$pid/stat is good, but we need remember
> the value of PF_KTHREAD is 0x00200000 and convert dec to hex.
> If we have no binary program and shell script which read
> /proc/$pid/stat, we can know it directly by
> `cat /proc/$pid/status`.
> 
> Signed-off-by: Chunguang Wu <fullspring2018@...il.com>
> ---
>  Documentation/filesystems/proc.rst | 2 ++
>  fs/proc/array.c                    | 7 +++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 9d5fd9424e8b..8a563684586c 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -179,6 +179,7 @@ read the file /proc/PID/status::
>    Gid:    100     100     100     100
>    FDSize: 256
>    Groups: 100 14 16
> +  Kthread:    0
>    VmPeak:     5004 kB
>    VmSize:     5004 kB
>    VmLck:         0 kB
> @@ -256,6 +257,7 @@ It's slow but very precise.
>   NSpid                       descendant namespace process ID hierarchy
>   NSpgid                      descendant namespace process group ID hierarchy
>   NSsid                       descendant namespace session ID hierarchy
> + Kthread                     kernel thread flag, 1 is yes, 0 is no
>   VmPeak                      peak virtual memory size
>   VmSize                      total program size
>   VmLck                       locked memory size

The Documentation changes look good, except that they may need to be moved
if you do the changes indicated below.


Now that I have looked at the rest of the patch:

> diff --git a/fs/proc/array.c b/fs/proc/array.c
> index 9b0315d34c58..fde6a0b92728 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -434,6 +434,13 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
>  
>  	task_state(m, ns, pid, task);
>  
> +	seq_puts(m, "Kthread:\t");
> +	if (task->flags & PF_KTHREAD) {
> +		seq_puts(m, "1\n");
> +	} else {
> +		seq_puts(m, "0\n");
> +	}
> +

I would put that patch fragment inside task_state(), but I'll leave that
to others to decide on.

and condense it to one line, e.g.:

	seq_puts(m, "Kthread: %c\n", task->flags & PF_KTHREAD ? '1' : '0');


>  	if (mm) {
>  		task_mem(m, mm);
>  		task_core_dumping(m, task);


Please add version info to your future patches.

Thanks.
-- 
~Randy