+ cgroup-use-irqsave-in-cgroup_rstat_flush_locked-fix.patch added to -mm tree

+ cgroup-use-irqsave-in-cgroup_rstat_flush_locked-fix.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: cgroup: add a comment to cgroup_rstat_flush_locked().
has been added to the -mm tree.  Its filename is
     cgroup-use-irqsave-in-cgroup_rstat_flush_locked-fix.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/cgroup-use-irqsave-in-cgroup_rstat_flush_locked-fix.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/cgroup-use-irqsave-in-cgroup_rstat_flush_locked-fix.patch

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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: cgroup: add a comment to cgroup_rstat_flush_locked().

Add a comment why spin_lock_irq() -> raw_spin_lock_irqsave() is needed.

Link: https://lkml.kernel.org/r/Yh+DOK73hfVV5ThX@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/cgroup/rstat.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/kernel/cgroup/rstat.c~cgroup-use-irqsave-in-cgroup_rstat_flush_locked-fix
+++ a/kernel/cgroup/rstat.c
@@ -155,6 +155,14 @@ static void cgroup_rstat_flush_locked(st
 		struct cgroup *pos = NULL;
 		unsigned long flags;
 
+		/*
+		 * The _irqsave() is needed because cgroup_rstat_lock is
+		 * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring
+		 * this lock with the _irq() suffix only disables interrupts on
+		 * a non-PREEMPT_RT kernel. The raw_spinlock_t below disables
+		 * interrupts on both configurations. The _irqsave() ensures
+		 * that interrupts are always disabled and later restored.
+		 */
 		raw_spin_lock_irqsave(cpu_lock, flags);
 		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
 			struct cgroup_subsys_state *css;
_

Patches currently in -mm which might be from bigeasy@linutronix.de are

mm-memcg-disable-threshold-event-handlers-on-preempt_rt.patch
mm-memcg-protect-per-cpu-counter-by-disabling-preemption-on-preempt_rt-where-needed.patch
mm-memcg-protect-memcg_stock-with-a-local_lock_t.patch
mm-memcg-disable-migration-instead-of-preemption-in-drain_all_stock.patch
mm-workingset-replace-irq-off-check-with-a-lockdep-assert.patch
cgroup-use-irqsave-in-cgroup_rstat_flush_locked.patch
cgroup-use-irqsave-in-cgroup_rstat_flush_locked-fix.patch