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memcg: fix mem_cgroup_move_lists locking

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Ever since the VM_BUG_ON(page_get_page_cgroup(page)) (now Bad page state) went
into page freeing, I've hit it from time to time in testing on some machines,
sometimes only after many days.  Recently found a machine which could usually
produce it within a few hours, which got me there at last.

The culprit is mem_cgroup_move_lists, whose locking is inadequate; and the
arrangement of structures was such that you got page_cgroups from the lru list
neatly put on to SLUB's freelist.  Kamezawa-san identified the same hole
independently.

The main problem was that it was missing the lock_page_cgroup it needs to
safely page_get_page_cgroup; but it's tricky to go beyond that too, and I
couldn't do it with SLAB_DESTROY_BY_RCU as I'd expected.  See the code for
comments on the constraints.

This patch immediately gets replaced by a simpler one from Hirokazu-san; but
is it just foolish pride that tells me to put this one on record, in case we
need to come back to it later?

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hirokazu Takahashi <taka@valinux.co.jp>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2008-03-04 14:29:13 -08:00 committed by Linus Torvalds
parent 6d48ff8bcf
commit 2680eed723
1 changed files with 43 additions and 6 deletions
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49
mm/memcontrol.c
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@ -277,6 +277,11 @@ static void lock_page_cgroup(struct page *page)
bit_spin_lock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
}
static int try_lock_page_cgroup(struct page *page)
{
return bit_spin_trylock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
}
static void unlock_page_cgroup(struct page *page)
{
bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
@ -348,17 +353,49 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
void mem_cgroup_move_lists(struct page *page, bool active)
{
struct page_cgroup *pc;
struct mem_cgroup *mem;
struct mem_cgroup_per_zone *mz;
unsigned long flags;
pc = page_get_page_cgroup(page);
if (!pc)
/*
* We cannot lock_page_cgroup while holding zone's lru_lock,
* because other holders of lock_page_cgroup can be interrupted
* with an attempt to rotate_reclaimable_page. But we cannot
* safely get to page_cgroup without it, so just try_lock it:
* mem_cgroup_isolate_pages allows for page left on wrong list.
*/
if (!try_lock_page_cgroup(page))
return;
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);
__mem_cgroup_move_lists(pc, active);
spin_unlock_irqrestore(&mz->lru_lock, flags);
/*
* Now page_cgroup is stable, but we cannot acquire mz->lru_lock
* while holding it, because mem_cgroup_force_empty_list does the
* reverse. Get a hold on the mem_cgroup before unlocking, so that
* the zoneinfo remains stable, then take mz->lru_lock; then check
* that page still points to pc and pc (even if freed and reassigned
* to that same page meanwhile) still points to the same mem_cgroup.
* Then we know mz still points to the right spinlock, so it's safe
* to move_lists (page->page_cgroup might be reset while we do so, but
* that doesn't matter: pc->page is stable till we drop mz->lru_lock).
* We're being a little naughty not to try_lock_page_cgroup again
* inside there, but we are safe, aren't we? Aren't we? Whistle...
*/
pc = page_get_page_cgroup(page);
if (pc) {
mem = pc->mem_cgroup;
mz = page_cgroup_zoneinfo(pc);
css_get(&mem->css);
unlock_page_cgroup(page);
spin_lock_irqsave(&mz->lru_lock, flags);
if (page_get_page_cgroup(page) == pc && pc->mem_cgroup == mem)
__mem_cgroup_move_lists(pc, active);
spin_unlock_irqrestore(&mz->lru_lock, flags);
css_put(&mem->css);
} else
unlock_page_cgroup(page);
}
/*