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[209.132.180.67]) by mx.google.com with ESMTP id a15si7449909eda.222.2019.09.23.15.30.26; Mon, 23 Sep 2019 15:30:49 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=fbb1qxEm; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391619AbfIVSs2 (ORCPT + 99 others); Sun, 22 Sep 2019 14:48:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:44964 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388599AbfIVSsP (ORCPT ); Sun, 22 Sep 2019 14:48:15 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D1D692190F; Sun, 22 Sep 2019 18:48:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569178094; bh=Iz/rm/WQRpcIwAOXL0oPExQ24VLEz8gHHqZ2wCq1jig=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fbb1qxEm6tgn+KDd8EQGvTJ8lDzbD9Txk0F3Q7e3mLjhTwHUZ/4n2iWHeVHFrzj3G UUwLYcSQcuDI7dNcE36jQRyxO4J64bWkyf2S1pV8EkJGTA8IZlpDXywyEdnC06at6r j8RSPig32e7ihuJoVW//bLg+zFWM3B00r3AxnaHc= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Kent Overstreet , Coly Li , Jens Axboe , Sasha Levin , linux-bcache@vger.kernel.org Subject: [PATCH AUTOSEL 5.3 159/203] closures: fix a race on wakeup from closure_sync Date: Sun, 22 Sep 2019 14:43:05 -0400 Message-Id: <20190922184350.30563-159-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190922184350.30563-1-sashal@kernel.org> References: <20190922184350.30563-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore 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