The patch titled
Subject: cgroup: use irqsave in cgroup_rstat_flush_locked().
has been removed from the -mm tree. Its filename was
cgroup-use-irqsave-in-cgroup_rstat_flush_locked.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx>
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/cgroup/rstat.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
--- a/kernel/cgroup/rstat.c~cgroup-use-irqsave-in-cgroup_rstat_flush_locked
+++ a/kernel/cgroup/rstat.c
@@ -153,8 +153,17 @@ 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);
+ /*
+ * 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;
@@ -166,7 +175,7 @@ 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@xxxxxxxxxxxxx are
