From: Johannes Weiner <hannes@cmpxchg.org>
Date: Wed, 10 Jun 2015 18:14:54 +0000 (-0700)
Subject: mm: memcontrol: fix false-positive VM_BUG_ON() on -rt
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=f371763a79d5212c2cb216b46fa8af46ba56cee3;p=sagit-ice-cold%2Fkernel_xiaomi_msm8998.git

mm: memcontrol: fix false-positive VM_BUG_ON() on -rt

On -rt, the VM_BUG_ON(!irqs_disabled()) triggers inside the memcg
swapout path because the spin_lock_irq(&mapping->tree_lock) in the
caller doesn't actually disable the hardware interrupts - which is fine,
because on -rt the tophalves run in process context and so we are still
safe from preemption while updating the statistics.

Remove the VM_BUG_ON() but keep the comment of what we rely on.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Clark Williams <williams@redhat.com>
Cc: Fernando Lopez-Lezcano <nando@ccrma.Stanford.EDU>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9da23a7ec4c0..a04225d372ba 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5835,9 +5835,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	if (!mem_cgroup_is_root(memcg))
 		page_counter_uncharge(&memcg->memory, 1);
 
-	/* XXX: caller holds IRQ-safe mapping->tree_lock */
-	VM_BUG_ON(!irqs_disabled());
-
+	/* Caller disabled preemption with mapping->tree_lock */
 	mem_cgroup_charge_statistics(memcg, page, -1);
 	memcg_check_events(memcg, page);
 }