From: Andrea Righi Date: Mon, 20 Feb 2012 12:11:49 +0000 (+0100) Subject: staging: zcache: avoid AB-BA deadlock condition X-Git-Tag: v3.3.1~170 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7e6373b36698068f2b0bb81ba4bdbf73c60096c5;p=thirdparty%2Fkernel%2Fstable.git staging: zcache: avoid AB-BA deadlock condition 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 Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c index ef7c52bb1df9f..dce04be1af30a 100644 --- 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 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); @@ -310,7 +312,6 @@ 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--; @@ -318,7 +319,6 @@ 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);