memcg: fix deadlock between lock_page_cgroup and mapping tree_lock

mapping->tree_lock can be acquired from interrupt context.  Then,
following dead lock can occur.

Assume "A" as a page.

 CPU0:
       lock_page_cgroup(A)
		interrupted
			-> take mapping->tree_lock.
 CPU1:
       take mapping->tree_lock
		-> lock_page_cgroup(A)

This patch tries to fix above deadlock by moving memcg's hook to out of
mapping->tree_lock.  charge/uncharge of pagecache/swapcache is protected
by page lock, not tree_lock.

After this patch, lock_page_cgroup() is not called under mapping->tree_lock.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 379ff0b..1b60f30 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -121,7 +121,6 @@ void __remove_from_page_cache(struct page *page)
 	mapping->nrpages--;
 	__dec_zone_page_state(page, NR_FILE_PAGES);
 	BUG_ON(page_mapped(page));
-	mem_cgroup_uncharge_cache_page(page);
 
 	/*
 	 * Some filesystems seem to re-dirty the page even after
@@ -145,6 +144,7 @@ void remove_from_page_cache(struct page *page)
 	spin_lock_irq(&mapping->tree_lock);
 	__remove_from_page_cache(page);
 	spin_unlock_irq(&mapping->tree_lock);
+	mem_cgroup_uncharge_cache_page(page);
 }
 
 static int sync_page(void *word)
@@ -476,13 +476,13 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 		if (likely(!error)) {
 			mapping->nrpages++;
 			__inc_zone_page_state(page, NR_FILE_PAGES);
+			spin_unlock_irq(&mapping->tree_lock);
 		} else {
 			page->mapping = NULL;
+			spin_unlock_irq(&mapping->tree_lock);
 			mem_cgroup_uncharge_cache_page(page);
 			page_cache_release(page);
 		}
-
-		spin_unlock_irq(&mapping->tree_lock);
 		radix_tree_preload_end();
 	} else
 		mem_cgroup_uncharge_cache_page(page);