Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753070AbaLFPXa (ORCPT ); Sat, 6 Dec 2014 10:23:30 -0500 Received: from ip4-83-240-67-251.cust.nbox.cz ([83.240.67.251]:47706 "EHLO ip4-83-240-18-248.cust.nbox.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752069AbaLFPIE (ORCPT ); Sat, 6 Dec 2014 10:08:04 -0500 From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Trond Myklebust , "J. Bruce Fields" , Jiri Slaby Subject: [PATCH 3.12 59/66] nfsd: Fix slot wake up race in the nfsv4.1 callback code Date: Sat, 6 Dec 2014 16:07:51 +0100 Message-Id: <55c8dd290be7ca4e64432b837d774314add709c0.1417878427.git.jslaby@suse.cz> X-Mailer: git-send-email 2.1.3 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Trond Myklebust 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit c6c15e1ed303ffc47e696ea1c9a9df1761c1f603 upstream. The currect code for nfsd41_cb_get_slot() and nfsd4_cb_done() has no locking in order to guarantee atomicity, and so allows for races of the form. Task 1 Task 2 ====== ====== if (test_and_set_bit(0) != 0) { clear_bit(0) rpc_wake_up_next(queue) rpc_sleep_on(queue) return false; } This patch breaks the race condition by adding a retest of the bit after the call to rpc_sleep_on(). Signed-off-by: Trond Myklebust Signed-off-by: J. Bruce Fields Signed-off-by: Jiri Slaby --- fs/nfsd/nfs4callback.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c index cc8c5b32043c..f42bbe5fbc0a 100644 --- a/fs/nfsd/nfs4callback.c +++ b/fs/nfsd/nfs4callback.c @@ -784,8 +784,12 @@ static bool nfsd41_cb_get_slot(struct nfs4_client *clp, struct rpc_task *task) { if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) { rpc_sleep_on(&clp->cl_cb_waitq, task, NULL); - dprintk("%s slot is busy\n", __func__); - return false; + /* Race breaker */ + if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) { + dprintk("%s slot is busy\n", __func__); + return false; + } + rpc_wake_up_queued_task(&clp->cl_cb_waitq, task); } return true; } -- 2.1.3 -- 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/