Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935402AbbDIKQB (ORCPT ); Thu, 9 Apr 2015 06:16:01 -0400 Received: from mail.kernel.org ([198.145.29.136]:40599 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755080AbbDIIuH (ORCPT ); Thu, 9 Apr 2015 04:50:07 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Trond Myklebust , "J. Bruce Fields" , Zefan Li Subject: [PATCH 3.4 009/176] nfsd: Fix slot wake up race in the nfsv4.1 callback code Date: Thu, 9 Apr 2015 16:44:17 +0800 Message-Id: <1428569224-23820-9-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1428569028-23762-1-git-send-email-lizf@kernel.org> References: <1428569028-23762-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1909 Lines: 59 From: Trond Myklebust 3.4.107-rc1 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: Zefan Li --- 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 c8e9f63..ebf3f59 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; } -- 1.9.1 -- 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/