From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20120330194826.611380821@linuxfoundation.org> Date: Fri, 30 Mar 2012 12:48:31 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Andrea Righi Subject: [ 006/175] staging: zcache: avoid AB-BA deadlock condition In-Reply-To: <20120330195801.GA31806@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andrea Righi 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 --- 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);