[BUGFIX v2] memcg: fix res_counter_read_u64 lock aware (Was Re: [PATCH] oom: handle overflow in mem_cgroup_out_of_memory()

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Thank you for advices. This version doesn't use inlined function
and adds no overhead in 64bit.

Info:
res_counter_read_u64 is not frequently called in memcontrol.c now.
It's called at user-interface and interaction with other components.
This addition of lock will not add any performance troubles.

==
res_counter_read_u64 reads u64 value without lock. It's dangerous
in 32bit environment. This patch adds lock.

Changelog:
 - handle 32/64 bit in other funciton
 - avoid unnecessary inlining.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 kernel/res_counter.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

Index: mmotm-0125/kernel/res_counter.c
===================================================================
--- mmotm-0125.orig/kernel/res_counter.c
+++ mmotm-0125/kernel/res_counter.c
@@ -126,10 +126,24 @@ ssize_t res_counter_read(struct res_coun
 			pos, buf, s - buf);
 }
 
+#if BITS_PER_LONG == 32
+u64 res_counter_read_u64(struct res_counter *counter, int member)
+{
+	unsigned long flags;
+	u64 ret;
+
+	spin_lock_irqsave(&counter->lock, flags);
+	ret = *res_counter_member(counter, member);
+	spin_unlock_irqrestore(&counter->lock, flags);
+
+	return ret;
+}
+#else
 u64 res_counter_read_u64(struct res_counter *counter, int member)
 {
 	return *res_counter_member(counter, member);
 }
+#endif
 
 int res_counter_memparse_write_strategy(const char *buf,
 					unsigned long long *res)

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