[PATCH] mm/memcontrol: Disable on PREEMPT_RT

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

From: Thomas Gleixner <tglx@linutronix.de>

MEMCG has a few constructs which are not compatible with PREEMPT_RT's
requirements. This includes:
- relying on disabled interrupts from spin_lock_irqsave() locking for
  something not related to lock itself (like the per-CPU counter).

- explicitly disabling interrupts and acquiring a spinlock_t based lock
  like in memcg_check_events() -> eventfd_signal().

- explicitly disabling interrupts and freeing memory like in
  drain_obj_stock() -> obj_cgroup_put() -> obj_cgroup_release() ->
  percpu_ref_exit().

Commit 559271146efc ("mm/memcg: optimize user context object stock
access") continued to optimize for the CPU local access which
complicates the PREEMPT_RT locking requirements further.

Disable MEMCG on PREEMPT_RT until the whole situation can be evaluated
again.

[ bigeasy: commit description. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 init/Kconfig |    1 +
 1 file changed, 1 insertion(+)

--- a/init/Kconfig
+++ b/init/Kconfig
@@ -943,6 +943,7 @@ config PAGE_COUNTER
 
 config MEMCG
 	bool "Memory controller"
+	depends on !PREEMPT_RT
 	select PAGE_COUNTER
 	select EVENTFD
 	help