From: Michael Jeanson <mjeanson@efficios.com>
Date: Mon, 4 Apr 2022 17:52:57 +0000 (-0400)
Subject: fix: sched/tracing: Don't re-read p->state when emitting sched_switch event (v5.18)
X-Git-Tag: v2.12.14~3
X-Git-Url: http://git.liburcu.org/?a=commitdiff_plain;h=7b023c37000c5c29fb30b7b795e1da280f08cfe5;hp=7b023c37000c5c29fb30b7b795e1da280f08cfe5;p=lttng-modules.git

fix: sched/tracing: Don't re-read p->state when emitting sched_switch event (v5.18)

See upstream commit :

  commit fa2c3254d7cfff5f7a916ab928a562d1165f17bb
  Author: Valentin Schneider <valentin.schneider@arm.com>
  Date:   Thu Jan 20 16:25:19 2022 +0000

    sched/tracing: Don't re-read p->state when emitting sched_switch event

    As of commit

      c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu")

    the following sequence becomes possible:

                          p->__state = TASK_INTERRUPTIBLE;
                          __schedule()
                            deactivate_task(p);
      ttwu()
        READ !p->on_rq
        p->__state=TASK_WAKING
                            trace_sched_switch()
                              __trace_sched_switch_state()
                                task_state_index()
                                  return 0;

    TASK_WAKING isn't in TASK_REPORT, so the task appears as TASK_RUNNING in
    the trace event.

    Prevent this by pushing the value read from __schedule() down the trace
    event.

Change-Id: I46743cd006be4b4d573cae2d77df7d6d16744d04
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---