The patch titled
memcg: correctly order reading PCG_USED and pc->mem_cgroup
has been added to the -mm tree. Its filename is
memcg-correctly-order-reading-pcg_used-and-pc-mem_cgroup.patch
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The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: memcg: correctly order reading PCG_USED and pc->mem_cgroup
From: Johannes Weiner <hannes@xxxxxxxxxxx>
The placement of the read-side barrier is confused: the writer first
sets pc->mem_cgroup, then PCG_USED. The read-side barrier has to be
between testing PCG_USED and reading pc->mem_cgroup.
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 27 +++++++++------------------
1 file changed, 9 insertions(+), 18 deletions(-)
diff -puN mm/memcontrol.c~memcg-correctly-order-reading-pcg_used-and-pc-mem_cgroup mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-correctly-order-reading-pcg_used-and-pc-mem_cgroup
+++ a/mm/memcontrol.c
@@ -836,13 +836,12 @@ void mem_cgroup_rotate_lru_list(struct p
return;
pc = lookup_page_cgroup(page);
- /*
- * Used bit is set without atomic ops but after smp_wmb().
- * For making pc->mem_cgroup visible, insert smp_rmb() here.
- */
- smp_rmb();
/* unused or root page is not rotated. */
- if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))
+ if (!PageCgroupUsed(pc))
+ return;
+ /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
+ smp_rmb();
+ if (mem_cgroup_is_root(pc->mem_cgroup))
return;
mz = page_cgroup_zoneinfo(pc);
list_move(&pc->lru, &mz->lists[lru]);
@@ -857,14 +856,10 @@ void mem_cgroup_add_lru_list(struct page
return;
pc = lookup_page_cgroup(page);
VM_BUG_ON(PageCgroupAcctLRU(pc));
- /*
- * Used bit is set without atomic ops but after smp_wmb().
- * For making pc->mem_cgroup visible, insert smp_rmb() here.
- */
- smp_rmb();
if (!PageCgroupUsed(pc))
return;
-
+ /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
+ smp_rmb();
mz = page_cgroup_zoneinfo(pc);
MEM_CGROUP_ZSTAT(mz, lru) += 1;
SetPageCgroupAcctLRU(pc);
@@ -1030,14 +1025,10 @@ mem_cgroup_get_reclaim_stat_from_page(st
return NULL;
pc = lookup_page_cgroup(page);
- /*
- * Used bit is set without atomic ops but after smp_wmb().
- * For making pc->mem_cgroup visible, insert smp_rmb() here.
- */
- smp_rmb();
if (!PageCgroupUsed(pc))
return NULL;
-
+ /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
+ smp_rmb();
mz = page_cgroup_zoneinfo(pc);
if (!mz)
return NULL;
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
mm-compaction-prevent-division-by-zero-during-user-requested-compaction.patch
mm-compaction-prevent-division-by-zero-during-user-requested-compaction-fix.patch
mm-compaction-prevent-division-by-zero-during-user-requested-compaction-fix-fix.patch
memcg-correctly-order-reading-pcg_used-and-pc-mem_cgroup.patch
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