This is a note to let you know that I've just added the patch titled
sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-tracing-report-task_rtlock_wait-tasks-as-task_.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit d51f543c8c1d5f17d92b8706783cede699bf4cdf
Author: Valentin Schneider <valentin.schneider@xxxxxxx>
Date: Thu Jan 20 16:25:20 2022 +0000
sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE
[ 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@xxxxxxxxxxxxxx>
Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220120162520.570782-3-valentin.schneider@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8fcf76fed984..031588cd2ccb 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1626,6 +1626,14 @@ 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);
}
