[RFC PATCH 6/9] sched: Treat try_to_block_task with pending signal as wakeup

Gabriele Monaco
2025-04-04T08:46:22Z

If a task sets itself to interruptible and schedules, the __schedule
function checks whether there's a pending signal and, if that's the
case, updates the state of the task to runnable instead of dequeuing.
By looking at the tracepoints, we see the task enters the scheduler
while sleepable but exits as runnable. From a modelling perspective,
this is equivalent to a wakeup and the tracepoints should reflect that.

Add the waking/wakeup tracepoints in the try_to_block_task function and
set the prev_state used by the sched_switch tracepoint to TASK_RUNNING
if the task had a pending signal and was not blocked.

Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
---
kernel/sched/core.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f2f79236d5811..48cb32abce01a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6584,7 +6584,12 @@ static bool try_to_block_task(struct rq *rq, struct task_struct *p,
int flags = DEQUEUE_NOCLOCK;

if (signal_pending_state(task_state, p)) {
- WRITE_ONCE(p->__state, TASK_RUNNING);
+ /*
+ * From a modelling perspective, this is equivalent to a wakeup
+ * before dequeuing the task: trace accordingly.
+ */
+ trace_sched_waking(p);
+ ttwu_do_wakeup(p);
return false;
}

@@ -6721,7 +6726,9 @@ static void __sched notrace __schedule(int sched_mode)
goto picked;
}
} else if (!preempt && prev_state) {
- try_to_block_task(rq, prev, prev_state);
+ /* Task was not blocked due to a signal and is again runnable */
+ if (!try_to_block_task(rq, prev, prev_state))
+ prev_state = TASK_RUNNING;
switch_count = &prev->nvcsw;
}

--
2.49.0