| From cfbc6a92212e74b07aa76c9e2f20c542e36077fb Mon Sep 17 00:00:00 2001 |
| From: Andrea Righi <andrea@betterlinux.com> |
| Date: Mon, 20 Feb 2012 13:11:49 +0100 |
| Subject: staging: zcache: avoid AB-BA deadlock condition |
| |
| From: Andrea Righi <andrea@betterlinux.com> |
| |
| commit cfbc6a92212e74b07aa76c9e2f20c542e36077fb upstream. |
| |
| Commit 9256a47 fixed a deadlock condition, being sure that the buddy |
| list spinlock is always taken before the page spinlock. |
| |
| However in zbud_free_and_delist() locking order is the opposite |
| (page lock -> list lock). |
| |
| Possible unsafe locking scenario (reported by lockdep): |
| |
| CPU0 CPU1 |
| ---- ---- |
| lock(&(&zbpg->lock)->rlock); |
| lock(zbud_budlists_spinlock); |
| lock(&(&zbpg->lock)->rlock); |
| lock(zbud_budlists_spinlock); |
| |
| Fix by grabbing the locks in opposite order in zbud_free_and_delist(). |
| |
| Signed-off-by: Andrea Righi <andrea@betterlinux.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/staging/zcache/zcache-main.c | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| --- a/drivers/staging/zcache/zcache-main.c |
| +++ b/drivers/staging/zcache/zcache-main.c |
| @@ -299,10 +299,12 @@ static void zbud_free_and_delist(struct |
| struct zbud_page *zbpg = |
| container_of(zh, struct zbud_page, buddy[budnum]); |
| |
| + spin_lock(&zbud_budlists_spinlock); |
| spin_lock(&zbpg->lock); |
| if (list_empty(&zbpg->bud_list)) { |
| /* ignore zombie page... see zbud_evict_pages() */ |
| spin_unlock(&zbpg->lock); |
| + spin_unlock(&zbud_budlists_spinlock); |
| return; |
| } |
| size = zbud_free(zh); |
| @@ -310,7 +312,6 @@ static void zbud_free_and_delist(struct |
| zh_other = &zbpg->buddy[(budnum == 0) ? 1 : 0]; |
| if (zh_other->size == 0) { /* was unbuddied: unlist and free */ |
| chunks = zbud_size_to_chunks(size) ; |
| - spin_lock(&zbud_budlists_spinlock); |
| BUG_ON(list_empty(&zbud_unbuddied[chunks].list)); |
| list_del_init(&zbpg->bud_list); |
| zbud_unbuddied[chunks].count--; |
| @@ -318,7 +319,6 @@ static void zbud_free_and_delist(struct |
| zbud_free_raw_page(zbpg); |
| } else { /* was buddied: move remaining buddy to unbuddied list */ |
| chunks = zbud_size_to_chunks(zh_other->size) ; |
| - spin_lock(&zbud_budlists_spinlock); |
| list_del_init(&zbpg->bud_list); |
| zcache_zbud_buddied_count--; |
| list_add_tail(&zbpg->bud_list, &zbud_unbuddied[chunks].list); |
