linux-kernel - [PATCH] psi: get poll_work to run when calling poll syscall next time

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Message-Id: <1563864339-2621-1-git-send-email-kerneljasonxing@linux.alibaba.com>
Date:   Tue, 23 Jul 2019 14:45:39 +0800
From:   Jason Xing <kerneljasonxing@...ux.alibaba.com>
To:     hannes@...xchg.org, surenb@...gle.com, mingo@...hat.com,
        peterz@...radead.org
Cc:     dennis@...nel.org, axboe@...nel.dk, lizefan@...wei.com,
        tj@...nel.org, kerneljasonxing@...ux.alibaba.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH] psi: get poll_work to run when calling poll syscall next time

Only when calling the poll syscall the first time can user
receive POLLPRI correctly. After that, user always fails to
acquire the event signal.

Reproduce case:
1. Get the monitor code in Documentation/accounting/psi.txt
2. Run it, and wait for the event triggered.
3. Kill and restart the process.

If the user doesn't kill the monitor process, it seems the
poll_work works fine. After killing and restarting the monitor,
the poll_work in kernel will never run again due to the wrong
value of poll_scheduled. Therefore, we should reset the value
as group_init() does after the last trigger is destroyed.

Signed-off-by: Jason Xing <kerneljasonxing@...ux.alibaba.com>
---
 kernel/sched/psi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7acc632..66f4385 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1133,6 +1133,12 @@ static void psi_trigger_destroy(struct kref *ref)
 	if (kworker_to_destroy) {
 		kthread_cancel_delayed_work_sync(&group->poll_work);
 		kthread_destroy_worker(kworker_to_destroy);
+		/*
+		 * The poll_work should have the chance to be put into the
+		 * kthread queue when calling poll syscall next time. So
+		 * reset poll_scheduled to zero as group_init() does
+		 */
+		atomic_set(&group->poll_scheduled, 0);
 	}
 	kfree(t);
 }
-- 
1.8.3.1