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Date: Wed, 11 Nov 2020 08:23:17 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Valentin Schneider <valentin.schneider@....com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched, lockdep: Annotate ->pi_lock recursion
The following commit has been merged into the sched/core branch of tip:
Commit-ID: ded467dc83ac7173f1532bb0faa25022ff8769e5
Gitweb: https://git.kernel.org/tip/ded467dc83ac7173f1532bb0faa25022ff8769e5
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 01 Oct 2020 16:13:01 +02:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 10 Nov 2020 18:39:01 +01:00
sched, lockdep: Annotate ->pi_lock recursion
There's a valid ->pi_lock recursion issue where the actual PI code
tries to wake up the stop task. Make lockdep aware so it doesn't
complain about this.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@....com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Link: https://lkml.kernel.org/r/20201023102347.406912197@infradead.org
---
kernel/sched/core.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6ea593c..9ce2fc7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2658,6 +2658,7 @@ int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)
void sched_set_stop_task(int cpu, struct task_struct *stop)
{
+ static struct lock_class_key stop_pi_lock;
struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
struct task_struct *old_stop = cpu_rq(cpu)->stop;
@@ -2673,6 +2674,20 @@ void sched_set_stop_task(int cpu, struct task_struct *stop)
sched_setscheduler_nocheck(stop, SCHED_FIFO, ¶m);
stop->sched_class = &stop_sched_class;
+
+ /*
+ * The PI code calls rt_mutex_setprio() with ->pi_lock held to
+ * adjust the effective priority of a task. As a result,
+ * rt_mutex_setprio() can trigger (RT) balancing operations,
+ * which can then trigger wakeups of the stop thread to push
+ * around the current task.
+ *
+ * The stop task itself will never be part of the PI-chain, it
+ * never blocks, therefore that ->pi_lock recursion is safe.
+ * Tell lockdep about this by placing the stop->pi_lock in its
+ * own class.
+ */
+ lockdep_set_class(&stop->pi_lock, &stop_pi_lock);
}
cpu_rq(cpu)->stop = stop;
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