[PATCH 5.17 0875/1126] sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE

Greg Kroah-Hartman
2022-04-05T08:37:13Z

From: Valentin Schneider <valentin.schneider@arm.com>

[ Upstream commit 25795ef6299f07ce3838f3253a9cb34f64efcfae ]

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

As pointed out by Eric, adding TASK_RTLOCK_WAIT to TASK_REPORT implies
exposing a new state to userspace tools which way not know what to do with
them. The only information that needs to be conveyed here is that a task is
waiting on an rt_mutex, which matches TASK_UNINTERRUPTIBLE - there's no
need for a new state.

Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20220120162520.570782-3-valentin.schneider@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/sched.h | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a76a178f8eb6..36e38434391c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1630,6 +1630,14 @@ static inline unsigned int __task_state_index(unsigned int tsk_state,
if (tsk_state == TASK_IDLE)
state = TASK_REPORT_IDLE;

+ /*
+ * We're lying here, but rather than expose a completely new task state
+ * to userspace, we can make this appear as if the task has gone through
+ * a regular rt_mutex_lock() call.
+ */
+ if (tsk_state == TASK_RTLOCK_WAIT)
+ state = TASK_UNINTERRUPTIBLE;
+
return fls(state);
}

--
2.34.1