[BUGFIX] 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>]

On Thu, 27 Jan 2011 09:24:34 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > 
> 
> I'll review. Against the roll-over, I think we just need to take lock.
> So, res_counter_read_u64() implementation was wrong. It should take lock.
> Please give me time.
> 

As far as I can see usages of return value of res_counter_read_u64()
in memcontrol.c, all values are handle in u64 and no >> PAGE_SHIFT
to 'int' is not done. I'll see usage of u64 return value to
functions in other files from memcontrol.c

But, at least, this patch is required, I think. There are races.

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

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 include/linux/res_counter.h |   13 ++++++++++++-
 kernel/res_counter.c        |    2 +-
 2 files changed, 13 insertions(+), 2 deletions(-)

Index: mmotm-0125/include/linux/res_counter.h
===================================================================
--- mmotm-0125.orig/include/linux/res_counter.h
+++ mmotm-0125/include/linux/res_counter.h
@@ -68,7 +68,18 @@ struct res_counter {
  * @pos:     and the offset.
  */
 
-u64 res_counter_read_u64(struct res_counter *counter, int member);
+u64 res_counter_read_u64_locked(struct res_counter *counter, int member);
+
+static inline 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_read_u64_locked(counter, member);
+	spin_unlock_irqrestore(&counter->lock, flags);
+	return ret;
+}
 
 ssize_t res_counter_read(struct res_counter *counter, int member,
 		const char __user *buf, size_t nbytes, loff_t *pos,
Index: mmotm-0125/kernel/res_counter.c
===================================================================
--- mmotm-0125.orig/kernel/res_counter.c
+++ mmotm-0125/kernel/res_counter.c
@@ -126,7 +126,7 @@ ssize_t res_counter_read(struct res_coun
 			pos, buf, s - buf);
 }
 
-u64 res_counter_read_u64(struct res_counter *counter, int member)
+u64 res_counter_read_u64_locked(struct res_counter *counter, int member)
 {
 	return *res_counter_member(counter, member);
 }

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