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=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 DF9A4C43331 for ; Sun, 10 Nov 2019 13:56:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BFA412085B for ; Sun, 10 Nov 2019 13:56:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726402AbfKJN4D (ORCPT ); Sun, 10 Nov 2019 08:56:03 -0500 Received: from vps-vb.mhejs.net ([37.28.154.113]:51690 "EHLO vps-vb.mhejs.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726390AbfKJN4D (ORCPT ); Sun, 10 Nov 2019 08:56:03 -0500 Received: from MUA by vps-vb.mhejs.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92.3) (envelope-from ) id 1iTngz-0000Y5-23; Sun, 10 Nov 2019 14:55:49 +0100 From: "Maciej S. Szmigiero" To: "Theodore Ts'o" Cc: Herbert Xu , Arnd Bergmann , Greg Kroah-Hartman , Sebastian Andrzej Siewior , Keerthy , Stephen Boyd , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] random: Don't freeze in add_hwgenerator_randomness() if stopping kthread Date: Sun, 10 Nov 2019 14:55:42 +0100 Message-Id: <20191110135543.3476097-1-mail@maciej.szmigiero.name> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org Since commit 59b569480dc8 ("random: Use wait_event_freezable() in add_hwgenerator_randomness()") there is a race in add_hwgenerator_randomness() between freezing and stopping the calling kthread. This commit changed wait_event_interruptible() call with kthread_freezable_should_stop() as a condition into wait_event_freezable() with just kthread_should_stop() as a condition to fix a warning that kthread_freezable_should_stop() might sleep inside the wait. wait_event_freezable() ultimately calls __refrigerator() with its check_kthr_stop argument set to false, which causes it to keep the kthread frozen even if somebody calls kthread_stop() on it. Calling wait_event_freezable() with kthread_should_stop() as a condition is racy because it doesn't take into account the situation where this condition becomes true on a kthread marked for freezing only after this condition has already been checked. Calling freezing() should avoid the issue that the commit 59b569480dc8 has fixed, as it is only a checking function, it doesn't actually do the freezing. add_hwgenerator_randomness() has two post-boot users: in khwrng the kthread will be frozen anyway by call to kthread_freezable_should_stop() in its main loop, while its second user (ath9k-hwrng) is not freezable at all. This change allows a VM with virtio-rng loaded to write s2disk image successfully. Fixes: 59b569480dc8 ("random: Use wait_event_freezable() in add_hwgenerator_randomness()") Signed-off-by: Maciej S. Szmigiero --- drivers/char/random.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index de434feb873a..2f87910dd498 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -2500,8 +2500,8 @@ void add_hwgenerator_randomness(const char *buffer, size_t count, * We'll be woken up again once below random_write_wakeup_thresh, * or when the calling thread is about to terminate. */ - wait_event_freezable(random_write_wait, - kthread_should_stop() || + wait_event_interruptible(random_write_wait, + kthread_should_stop() || freezing(current) || ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits); mix_pool_bytes(poolp, buffer, count); credit_entropy_bits(poolp, entropy);