From cfbc6a92212e74b07aa76c9e2f20c542e36077fb Mon Sep 17 00:00:00 2001 From: Andrea Righi Date: Mon, 20 Feb 2012 13:11:49 +0100 Subject: [PATCH] staging: zcache: avoid AB-BA deadlock condition 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 Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/staging/zcache/zcache-main.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c index d7020b774039..238d82095ab1 100644 --- a/drivers/staging/zcache/zcache-main.c +++ b/drivers/staging/zcache/zcache-main.c @@ -333,10 +333,12 @@ static void zbud_free_and_delist(struct zbud_hdr *zh) 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); @@ -344,7 +346,6 @@ static void zbud_free_and_delist(struct zbud_hdr *zh) 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--; @@ -352,7 +353,6 @@ static void zbud_free_and_delist(struct zbud_hdr *zh) 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);