lkml.org 
[lkml]   [2020]   [Nov]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
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@infradead.org>
AuthorDate: Thu, 01 Oct 2020 16:13:01 +02:00
Committer: Peter Zijlstra <peterz@infradead.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@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.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, &param);

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;
\
 
 \ /
  Last update: 2020-11-11 09:25    [W:0.566 / U:0.512 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site