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Commit 713735b4 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
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memcg: correctly order reading PCG_USED and pc->mem_cgroup 



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: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2550326a

mm/memcontrol.c

+9 −18
Original line number Diff line number Diff line
@@ -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;