Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753508Ab2BTML6 (ORCPT ); Mon, 20 Feb 2012 07:11:58 -0500 Received: from mail.betterlinux.com ([199.58.199.50]:38059 "EHLO mail.betterlinux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751129Ab2BTML5 (ORCPT ); Mon, 20 Feb 2012 07:11:57 -0500 X-DKIM: OpenDKIM Filter v2.4.1 mail.betterlinux.com 2EAF282A0D From: Andrea Righi To: Greg Kroah-Hartman Cc: Dan Magenheimer , Seth Jennings , devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, stable@kernel.org Subject: [PATCH] zcache: avoid AB-BA deadlock condition Date: Mon, 20 Feb 2012 13:11:49 +0100 Message-Id: <1329739909-3174-1-git-send-email-andrea@betterlinux.com> X-Mailer: git-send-email 1.7.5.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2438 Lines: 63 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 --- drivers/staging/zcache/zcache-main.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c index ef7c52b..dce04be 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); -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/