memcg: fix deadlock by inverting lrucare nesting
We have forgotten the rules of lock nesting: the irq-safe ones must be
taken inside the non-irq-safe ones, otherwise we are open to deadlock:
CPU0 CPU1
---- ----
lock(&(&pc->lock)->rlock);
local_irq_disable();
lock(&(&zone->lru_lock)->rlock);
lock(&(&pc->lock)->rlock);
<Interrupt>
lock(&(&zone->lru_lock)->rlock);
To check a different locking issue, I happened to add a spin_lock to
memcg's bit_spin_lock in lock_page_cgroup(), and lockdep very quickly
complained about __mem_cgroup_commit_charge_lrucare() (on CPU1 above).
So delete __mem_cgroup_commit_charge_lrucare(), passing a bool lrucare to
__mem_cgroup_commit_charge() instead, taking zone->lru_lock under
lock_page_cgroup() in the lrucare case.
The original was using spin_lock_irqsave, but we'd be in more trouble if
it were ever called at interrupt time: unconditional _irq is enough. And
ClearPageLRU before del from lru, SetPageLRU before add to lru: no strong
reason, but that is the ordering used consistently elsewhere.
Fixes 36b62ad539498d00c2d280a151a ("memcg: simplify corner case handling
of LRU").
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 228d646..1097d80 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2408,8 +2408,12 @@
struct page *page,
unsigned int nr_pages,
struct page_cgroup *pc,
- enum charge_type ctype)
+ enum charge_type ctype,
+ bool lrucare)
{
+ struct zone *uninitialized_var(zone);
+ bool was_on_lru = false;
+
lock_page_cgroup(pc);
if (unlikely(PageCgroupUsed(pc))) {
unlock_page_cgroup(pc);
@@ -2420,6 +2424,21 @@
* we don't need page_cgroup_lock about tail pages, becase they are not
* accessed by any other context at this point.
*/
+
+ /*
+ * In some cases, SwapCache and FUSE(splice_buf->radixtree), the page
+ * may already be on some other mem_cgroup's LRU. Take care of it.
+ */
+ if (lrucare) {
+ zone = page_zone(page);
+ spin_lock_irq(&zone->lru_lock);
+ if (PageLRU(page)) {
+ ClearPageLRU(page);
+ del_page_from_lru_list(zone, page, page_lru(page));
+ was_on_lru = true;
+ }
+ }
+
pc->mem_cgroup = memcg;
/*
* We access a page_cgroup asynchronously without lock_page_cgroup().
@@ -2443,9 +2462,18 @@
break;
}
+ if (lrucare) {
+ if (was_on_lru) {
+ VM_BUG_ON(PageLRU(page));
+ SetPageLRU(page);
+ add_page_to_lru_list(zone, page, page_lru(page));
+ }
+ spin_unlock_irq(&zone->lru_lock);
+ }
+
mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), nr_pages);
unlock_page_cgroup(pc);
- WARN_ON_ONCE(PageLRU(page));
+
/*
* "charge_statistics" updated event counter. Then, check it.
* Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
@@ -2643,7 +2671,7 @@
ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
if (ret == -ENOMEM)
return ret;
- __mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype);
+ __mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype, false);
return 0;
}
@@ -2663,35 +2691,6 @@
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
enum charge_type ctype);
-static void
-__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *memcg,
- enum charge_type ctype)
-{
- struct page_cgroup *pc = lookup_page_cgroup(page);
- struct zone *zone = page_zone(page);
- unsigned long flags;
- bool removed = false;
-
- /*
- * In some case, SwapCache, FUSE(splice_buf->radixtree), the page
- * is already on LRU. It means the page may on some other page_cgroup's
- * LRU. Take care of it.
- */
- spin_lock_irqsave(&zone->lru_lock, flags);
- if (PageLRU(page)) {
- del_page_from_lru_list(zone, page, page_lru(page));
- ClearPageLRU(page);
- removed = true;
- }
- __mem_cgroup_commit_charge(memcg, page, 1, pc, ctype);
- if (removed) {
- add_page_to_lru_list(zone, page, page_lru(page));
- SetPageLRU(page);
- }
- spin_unlock_irqrestore(&zone->lru_lock, flags);
- return;
-}
-
int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask)
{
@@ -2769,13 +2768,16 @@
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
enum charge_type ctype)
{
+ struct page_cgroup *pc;
+
if (mem_cgroup_disabled())
return;
if (!memcg)
return;
cgroup_exclude_rmdir(&memcg->css);
- __mem_cgroup_commit_charge_lrucare(page, memcg, ctype);
+ pc = lookup_page_cgroup(page);
+ __mem_cgroup_commit_charge(memcg, page, 1, pc, ctype, true);
/*
* Now swap is on-memory. This means this page may be
* counted both as mem and swap....double count.
@@ -3248,7 +3250,7 @@
ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
else
ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
- __mem_cgroup_commit_charge(memcg, newpage, 1, pc, ctype);
+ __mem_cgroup_commit_charge(memcg, newpage, 1, pc, ctype, false);
return ret;
}
@@ -3332,7 +3334,7 @@
* the newpage may be on LRU(or pagevec for LRU) already. We lock
* LRU while we overwrite pc->mem_cgroup.
*/
- __mem_cgroup_commit_charge_lrucare(newpage, memcg, type);
+ __mem_cgroup_commit_charge(memcg, newpage, 1, pc, type, true);
}
#ifdef CONFIG_DEBUG_VM