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

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

[Andrew Morton]

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

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

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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: cgroup: use irqsave in cgroup_rstat_flush_locked().

All callers of cgroup_rstat_flush_locked() acquire cgroup_rstat_lock
either with spin_lock_irq() or spin_lock_irqsave(). 
cgroup_rstat_flush_locked() itself acquires cgroup_rstat_cpu_lock which is
a raw_spin_lock.  This lock is also acquired in cgroup_rstat_updated() in
IRQ context and therefore requires _irqsave() locking suffix in
cgroup_rstat_flush_locked().

Since there is no difference between spin_lock_t and raw_spin_lock_t on
!RT lockdep does not complain here.  On RT lockdep complains because the
interrupts were not disabled here and a deadlock is possible.

Acquire the raw_spin_lock_t with disabled interrupts.

Link: https://lkml.kernel.org/r/20220301122143.1521823-2-bigeasy@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.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 |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/cgroup/rstat.c~cgroup-use-irqsave-in-cgroup_rstat_flush_locked
+++ a/kernel/cgroup/rstat.c
@@ -153,8 +153,9 @@ static void cgroup_rstat_flush_locked(st
 		raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock,
 						       cpu);
 		struct cgroup *pos = NULL;
+		unsigned long flags;
 
-		raw_spin_lock(cpu_lock);
+		raw_spin_lock_irqsave(cpu_lock, flags);
 		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
 			struct cgroup_subsys_state *css;
 
@@ -166,7 +167,7 @@ static void cgroup_rstat_flush_locked(st
 				css->ss->css_rstat_flush(css, cpu);
 			rcu_read_unlock();
 		}
-		raw_spin_unlock(cpu_lock);
+		raw_spin_unlock_irqrestore(cpu_lock, flags);
 
 		/* if @may_sleep, play nice and yield if necessary */
 		if (may_sleep && (need_resched() ||
_

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
cgroup-use-irqsave-in-cgroup_rstat_flush_locked.patch
mm-workingset-replace-irq-off-check-with-a-lockdep-assert.patch