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memcg: correctly order reading PCG_USED and pc->mem_cgroup

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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@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2011-01-20 14:44:31 -08:00 committed by Linus Torvalds
parent 2550326ac7
commit 713735b423
1 changed files with 9 additions and 18 deletions
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27
mm/memcontrol.c
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@ -836,13 +836,12 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
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 *page, enum lru_list lru)
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);
/* huge page split is done under lru_lock. so, we have no races. */
MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
@ -1031,14 +1026,10 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
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;