[PATCH v2 2/2] sched/tracing: Add TASK_RTLOCK_WAIT to TASK_REPORT

From: Valentin Schneider
Date: Mon Jan 17 2022 - 11:51:49 EST


TASK_RTLOCK_WAIT currently isn't part of TASK_REPORT, thus a task blocking
on an rtlock will appear as having a task state == 0, IOW TASK_RUNNING.

The actual state is saved in p->saved_state, but reading it after reading
p->__state has a few issues:
o that could still be TASK_RUNNING in the case of e.g. rt_spin_lock
o ttwu_state_match() might have changed that to TASK_RUNNING

Add TASK_RTLOCK_WAIT to TASK_REPORT.

Reported-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
fs/proc/array.c | 3 ++-
include/linux/sched.h | 17 +++++++++--------
include/trace/events/sched.h | 1 +
3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index ff869a66b34e..f4cae65529a6 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -128,9 +128,10 @@ static const char * const task_state_array[] = {
"X (dead)", /* 0x10 */
"Z (zombie)", /* 0x20 */
"P (parked)", /* 0x40 */
+ "L (rt-locked)", /* 0x80 */

/* states beyond TASK_REPORT: */
- "I (idle)", /* 0x80 */
+ "I (idle)", /* 0x100 */
};

static inline const char *get_task_state(struct task_struct *tsk)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d00837d12b9d..18fd77578dae 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -91,13 +91,14 @@ struct task_group;
#define EXIT_TRACE (EXIT_ZOMBIE | EXIT_DEAD)
/* Used in tsk->state again: */
#define TASK_PARKED 0x0040
-#define TASK_DEAD 0x0080
-#define TASK_WAKEKILL 0x0100
-#define TASK_WAKING 0x0200
-#define TASK_NOLOAD 0x0400
-#define TASK_NEW 0x0800
/* RT specific auxilliary flag to mark RT lock waiters */
-#define TASK_RTLOCK_WAIT 0x1000
+#define TASK_RTLOCK_WAIT 0x0080
+
+#define TASK_DEAD 0x0100
+#define TASK_WAKEKILL 0x0200
+#define TASK_WAKING 0x0400
+#define TASK_NOLOAD 0x0800
+#define TASK_NEW 0x1000
#define TASK_STATE_MAX 0x2000

/* Convenience macros for the sake of set_current_state: */
@@ -114,7 +115,7 @@ struct task_group;
#define TASK_REPORT (TASK_RUNNING | TASK_INTERRUPTIBLE | \
TASK_UNINTERRUPTIBLE | __TASK_STOPPED | \
__TASK_TRACED | EXIT_DEAD | EXIT_ZOMBIE | \
- TASK_PARKED)
+ TASK_PARKED | TASK_RTLOCK_WAIT)

#define task_is_running(task) (READ_ONCE((task)->__state) == TASK_RUNNING)

@@ -1636,7 +1637,7 @@ static inline unsigned int task_state_index(struct task_struct *tsk)

static inline char task_index_to_char(unsigned int state)
{
- static const char state_char[] = "RSDTtXZPI";
+ static const char state_char[] = "RSDTtXZPLI";

BUILD_BUG_ON(1 + ilog2(TASK_REPORT_MAX) != sizeof(state_char) - 1);

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 65e786756321..f86ec9af19ff 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -261,6 +261,7 @@ TRACE_EVENT(sched_switch,
{ EXIT_DEAD, "X" },
{ EXIT_ZOMBIE, "Z" },
{ TASK_PARKED, "P" },
+ { TASK_RTLOCK_WAIT, "L" },
{ TASK_DEAD, "I" }) :
"R",

--
2.25.1