linux-kernel - [PATCH v7 3/3] procfs: treat parked tasks as sleeping for task state

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Message-ID: <1428698900-13358-3-git-send-email-cmetcalf@ezchip.com>
Date:	Fri, 10 Apr 2015 16:48:20 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Jones <drjones@...hat.com>,
	chai wen <chaiw.fnst@...fujitsu.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Fabian Frederick <fabf@...net.be>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ben Zhang <benzh@...omium.org>,
	"Christoph Lameter" <cl@...ux.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	<linux-kernel@...r.kernel.org>, "Jonathan Corbet" <corbet@....net>,
	<linux-doc@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Chris Metcalf <cmetcalf@...hip.com>
Subject: [PATCH v7 3/3] procfs: treat parked tasks as sleeping for task state

Allowing watchdog threads to be parked means that we now have the
opportunity of actually seeing persistent parked threads in the output
of /proc's stat and status files.  The existing code reported such
threads as "Running", which is kind-of true if you think of the case
where we park them as part of taking cpus offline.  But if we allow
parking them indefinitely, "Running" is pretty misleading, so we report
them as "Sleeping" instead.

We could simply report them with a new string, "Parked", but it feels
like it's a bit risky for userspace to see unexpected new values.
The scheduler does report parked tasks with a "P" in debugging output
from sched_show_task() or dump_cpu_task(), but that's a different API.

This change seemed slightly cleaner than updating the task_state_array
to have additional rows.  TASK_DEAD should be subsumed by the exit_state
bits; TASK_WAKEKILL is just a modifier; and TASK_WAKING can very
reasonably be reported as "Running" (as it is now).  Only TASK_PARKED
shows up with unreasonable output here.

Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
---
 fs/proc/array.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index a3893b7505b2..2eb623ffb0b7 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -126,6 +126,10 @@ static inline const char *get_task_state(struct task_struct *tsk)
 {
 	unsigned int state = (tsk->state | tsk->exit_state) & TASK_REPORT;

+	/* Treat parked tasks as sleeping. */
+	if (state == TASK_PARKED)
+		state = TASK_SLEEPING;
+
 	BUILD_BUG_ON(1 + ilog2(TASK_REPORT) != ARRAY_SIZE(task_state_array)-1);

 	return task_state_array[fls(state)];
-- 
2.1.2

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