[4.2.y-ckt stable] Patch "memcg: fix thresholds for 32b architectures." has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    memcg: fix thresholds for 32b architectures.

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 6e58256c739770ccc8aec2c8e2c49fff52fdead3 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko at suse.com>
Date: Thu, 5 Nov 2015 18:50:29 -0800
Subject: memcg: fix thresholds for 32b architectures.

commit c12176d3368b9b36ae484d323d41e94be26f9b65 upstream.

Commit 424cdc141380 ("memcg: convert threshold to bytes") has fixed a
regression introduced by 3e32cb2e0a12 ("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 424cdc141380 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: 424cdc141380 ("memcg: convert threshold to bytes")
Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
Signed-off-by: Michal Hocko <mhocko at suse.com>
Reported-by: Ben Hutchings <ben at decadent.org.uk>
Reviewed-by: Vladimir Davydov <vdavydov at virtuozzo.com>
Acked-by: Johannes Weiner <hannes at cmpxchg.org>
From: Michal Hocko <mhocko at kernel.org>
Subject: memcg-fix-thresholds-for-32b-architectures-fix

Cc: Ben Hutchings <ben at decadent.org.uk>
Cc: Vladimir Davydov <vdavydov at virtuozzo.com>
Cc: Johannes Weiner <hannes at cmpxchg.org>
From: Andrew Morton <akpm at 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 at decadent.org.uk>
Cc: Johannes Weiner <hannes at cmpxchg.org>
Cc: Michal Hocko <mhocko at kernel.org>
Cc: Vladimir Davydov <vdavydov at virtuozzo.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/memcontrol.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 03a6f75..364f972 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3136,9 +3136,9 @@ 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);
@@ -3151,7 +3151,7 @@ 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 {
@@ -3185,9 +3185,9 @@ 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;
@@ -3687,7 +3687,6 @@ 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);

--
1.9.1