memcg: fix thresholds for 32b architectures.

Commit 424cdc14 ("memcg: convert threshold to bytes") has fixed a
regression introduced by 3e32cb2e ("mm: memcontrol: lockless page
counters") where thresholds were silently converted to use page units
rather than bytes when interpreting the user input.

The fix is not complete, though, as properly pointed out by Ben Hutchings
during stable backport review.  The page count is converted to bytes but
unsigned long is used to hold the value which would be obviously not
sufficient for 32b systems with more than 4G thresholds.  The same applies
to usage as taken from mem_cgroup_usage which might overflow.

Let's remove this bytes vs.  pages internal tracking differences and
handle thresholds in page units internally.  Chage mem_cgroup_usage() to
return the value in page units and revert 424cdc14 because this should
be sufficient for the consistent handling.  mem_cgroup_read_u64 as the
only users of mem_cgroup_usage outside of the threshold handling code is
converted to give the proper in bytes result.  It is doing that already
for page_counter output so this is more consistent as well.

The value presented to the userspace is still in bytes units.

Fixes: 424cdc14 ("memcg: convert threshold to bytes")
Fixes: 3e32cb2e ("mm: memcontrol: lockless page counters")
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
From: Michal Hocko <mhocko@kernel.org>
Subject: memcg-fix-thresholds-for-32b-architectures-fix

Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
From: Andrew Morton <akpm@linux-foundation.org>
Subject: memcg-fix-thresholds-for-32b-architectures-fix-fix

don't attempt to inline mem_cgroup_usage()

The compiler ignores the inline anwyay.  And __always_inlining it adds 600
bytes of goop to the .o file.

Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2801,9 +2801,9 @@ static unsigned long tree_stat(struct mem_cgroup *memcg,
 	return val;
 }
 
-static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
+static inline unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
 {
-	u64 val;
+	unsigned long val;
 
 	if (mem_cgroup_is_root(memcg)) {
 		val = tree_stat(memcg, MEM_CGROUP_STAT_CACHE);
@@ -2816,7 +2816,7 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
 		else
 			val = page_counter_read(&memcg->memsw);
 	}
-	return val << PAGE_SHIFT;
+	return val;
 }
 
 enum {
@@ -2850,9 +2850,9 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
 	switch (MEMFILE_ATTR(cft->private)) {
 	case RES_USAGE:
 		if (counter == &memcg->memory)
-			return mem_cgroup_usage(memcg, false);
+			return (u64)mem_cgroup_usage(memcg, false) * PAGE_SIZE;
 		if (counter == &memcg->memsw)
-			return mem_cgroup_usage(memcg, true);
+			return (u64)mem_cgroup_usage(memcg, true) * PAGE_SIZE;
 		return (u64)page_counter_read(counter) * PAGE_SIZE;
 	case RES_LIMIT:
 		return (u64)counter->limit * PAGE_SIZE;
@@ -3352,7 +3352,6 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
 	ret = page_counter_memparse(args, "-1", &threshold);
 	if (ret)
 		return ret;
-	threshold <<= PAGE_SHIFT;
 
 	mutex_lock(&memcg->thresholds_lock);