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

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Date:   Sat, 15 Apr 2023 16:21:55 +0800
From:   Chunguang Wu <fullspring2018@...il.com>
To:     akpm@...ux-foundation.org, corbet@....net
Cc:     adobriyan@...il.com, rdunlap@...radead.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: [PATCH] fs/proc: add Kthread flag to /proc/$pid/status

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
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");
+	}
+
 	if (mm) {
 		task_mem(m, mm);
 		task_core_dumping(m, task);
-- 
2.39.1