Commit 52dbb905 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
Browse files

memcg: fix race at move_parent around compound_order() 



A fix up mem_cgroup_move_parent() which use compound_order() in
asynchronous manner.  This compound_order() may return unknown value
because we don't take lock.  Use PageTransHuge() and HPAGE_SIZE instead
of it.

Also clean up for mem_cgroup_move_parent().
 - remove unnecessary initialization of local variable.
 - rename charge_size -> page_size
 - remove unnecessary (wrong) comment.
 - added a comment about THP.

Note:
 Current design take compound_page_lock() in caller of move_account().
 This should be revisited when we implement direct move_task of hugepage
 without splitting.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3d37c4a9

mm/memcontrol.c

+16 −9
Original line number Diff line number Diff line
@@ -2236,7 +2236,12 @@ static int mem_cgroup_move_account(struct page_cgroup *pc, 
{

	int ret = -EINVAL;

	unsigned long flags;



	/*

	 * The page is isolated from LRU. So, collapse function

	 * will not handle this page. But page splitting can happen.

	 * Do this check under compound_page_lock(). The caller should

	 * hold it.

	 */

	if ((charge_size > PAGE_SIZE) && !PageTransHuge(pc->page))

		return -EBUSY;
@@ -2268,7 +2273,7 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc, 
	struct cgroup *cg = child->css.cgroup;

	struct cgroup *pcg = cg->parent;

	struct mem_cgroup *parent;

	int charge = PAGE_SIZE;

	int page_size = PAGE_SIZE;

	unsigned long flags;

	int ret;
@@ -2281,22 +2286,24 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc, 
		goto out;

	if (isolate_lru_page(page))

		goto put;

	/* The page is isolated from LRU and we have no race with splitting */

	charge = PAGE_SIZE << compound_order(page);



	if (PageTransHuge(page))

		page_size = HPAGE_SIZE;



	parent = mem_cgroup_from_cont(pcg);

	ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, charge);

	ret = __mem_cgroup_try_charge(NULL, gfp_mask,

				&parent, false, page_size);

	if (ret || !parent)

		goto put_back;



	if (charge > PAGE_SIZE)

	if (page_size > PAGE_SIZE)

		flags = compound_lock_irqsave(page);



	ret = mem_cgroup_move_account(pc, child, parent, true, charge);

	ret = mem_cgroup_move_account(pc, child, parent, true, page_size);

	if (ret)

		mem_cgroup_cancel_charge(parent, charge);

		mem_cgroup_cancel_charge(parent, page_size);



	if (charge > PAGE_SIZE)

	if (page_size > PAGE_SIZE)

		compound_unlock_irqrestore(page, flags);

put_back:

	putback_lru_page(page);

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