From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 37131C10F14 for ; Thu, 3 Oct 2019 17:19:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 00B7E20865 for ; Thu, 3 Oct 2019 17:19:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570123160; bh=Iz/rm/WQRpcIwAOXL0oPExQ24VLEz8gHHqZ2wCq1jig=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=DBBrl6Kw779nIKfsFD7zH+OfSf+E4erR9avUi1f4Q23Z9BpOCZR6dcsei800CDMH8 UeTmGGPZw53xsc6/y9pj4D3N+Ac+ikxK7EXjmNHqObJc6sf5Lhdn9FRcNbgdhvl1rc PSdCDojD/WiyuhIEcoInWUGtywmfGAfS1XsBWagU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388915AbfJCQT5 (ORCPT ); Thu, 3 Oct 2019 12:19:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:47154 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388597AbfJCQTy (ORCPT ); Thu, 3 Oct 2019 12:19:54 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 030EF215EA; Thu, 3 Oct 2019 16:19:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570119593; bh=Iz/rm/WQRpcIwAOXL0oPExQ24VLEz8gHHqZ2wCq1jig=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GT+kXmouK28GwBhXxQJVlO8agg2JRadozt4J48Eu1/AUpc2Q4czDGXEni9aYrZoJ7 4/x0hmRkDXVlLsA/MS1KkwpyHxzVfORdTx1bxfCjcK6LqzogozdhcK9mwZzzQi0p5M KXURU0zKMJ2yt6rmxrOJdepSGLLp/pEhs2IcIOC8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kent Overstreet , Coly Li , Jens Axboe , Sasha Levin Subject: [PATCH 4.19 123/211] closures: fix a race on wakeup from closure_sync Date: Thu, 3 Oct 2019 17:53:09 +0200 Message-Id: <20191003154515.136772999@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191003154447.010950442@linuxfoundation.org> References: <20191003154447.010950442@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kent Overstreet [ Upstream commit a22a9602b88fabf10847f238ff81fde5f906fef7 ] The race was when a thread using closure_sync() notices cl->s->done == 1 before the thread calling closure_put() calls wake_up_process(). Then, it's possible for that thread to return and exit just before wake_up_process() is called - so we're trying to wake up a process that no longer exists. rcu_read_lock() is sufficient to protect against this, as there's an rcu barrier somewhere in the process teardown path. Signed-off-by: Kent Overstreet Acked-by: Coly Li Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- drivers/md/bcache/closure.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/md/bcache/closure.c b/drivers/md/bcache/closure.c index 73f5319295bc9..c12cd809ab193 100644 --- a/drivers/md/bcache/closure.c +++ b/drivers/md/bcache/closure.c @@ -105,8 +105,14 @@ struct closure_syncer { static void closure_sync_fn(struct closure *cl) { - cl->s->done = 1; - wake_up_process(cl->s->task); + struct closure_syncer *s = cl->s; + struct task_struct *p; + + rcu_read_lock(); + p = READ_ONCE(s->task); + s->done = 1; + wake_up_process(p); + rcu_read_unlock(); } void __sched __closure_sync(struct closure *cl) -- 2.20.1