Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:55582 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756792AbaKSUtO (ORCPT ); Wed, 19 Nov 2014 15:49:14 -0500 Date: Wed, 19 Nov 2014 15:49:14 -0500 From: Bruce Fields To: Trond Myklebust Cc: linux-nfs@vger.kernel.org Subject: Re: [PATCH] nfsd: Fix slot wake up race in the nfsv4.1 callback code Message-ID: <20141119204914.GA14207@fieldses.org> References: <1416419270-8964-1-git-send-email-trond.myklebust@primarydata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1416419270-8964-1-git-send-email-trond.myklebust@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Nov 19, 2014 at 12:47:50PM -0500, Trond Myklebust wrote: > 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. Makes sense, thanks. Applying for 3.18 and stable. --b. > > 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 > Cc: stable@vger.kernel.org > --- > 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 ed2b1151b171..7cbdf1b2e4ab 100644 > --- a/fs/nfsd/nfs4callback.c > +++ b/fs/nfsd/nfs4callback.c > @@ -774,8 +774,12 @@ 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; > } > -- > 1.9.3 >