From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:55480 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390166AbeKTDRR (ORCPT ); Mon, 19 Nov 2018 22:17:17 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Miklos Szeredi Subject: [PATCH 4.9 20/83] fuse: fix blocked_waitq wakeup Date: Mon, 19 Nov 2018 17:28:46 +0100 Message-Id: <20181119162615.868998569@linuxfoundation.org> In-Reply-To: <20181119162612.046511542@linuxfoundation.org> References: <20181119162612.046511542@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Miklos Szeredi commit 908a572b80f6e9577b45e81b3dfe2e22111286b8 upstream. Using waitqueue_active() is racy. Make sure we issue a wake_up() unconditionally after storing into fc->blocked. After that it's okay to optimize with waitqueue_active() since the first wake up provides the necessary barrier for all waiters, not the just the woken one. Signed-off-by: Miklos Szeredi Fixes: 3c18ef8117f0 ("fuse: optimize wake_up") Cc: # v3.10 Signed-off-by: Greg Kroah-Hartman --- fs/fuse/dev.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -383,12 +383,19 @@ static void request_end(struct fuse_conn if (test_bit(FR_BACKGROUND, &req->flags)) { spin_lock(&fc->lock); clear_bit(FR_BACKGROUND, &req->flags); - if (fc->num_background == fc->max_background) + if (fc->num_background == fc->max_background) { fc->blocked = 0; - - /* Wake up next waiter, if any */ - if (!fc->blocked && waitqueue_active(&fc->blocked_waitq)) wake_up(&fc->blocked_waitq); + } else if (!fc->blocked) { + /* + * Wake up next waiter, if any. It's okay to use + * waitqueue_active(), as we've already synced up + * fc->blocked with waiters with the wake_up() call + * above. + */ + if (waitqueue_active(&fc->blocked_waitq)) + wake_up(&fc->blocked_waitq); + } if (fc->num_background == fc->congestion_threshold && fc->connected && fc->bdi_initialized) {