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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 4EEEFC433EF for ; Thu, 23 Sep 2021 16:04:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 36E736103C for ; Thu, 23 Sep 2021 16:04:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242408AbhIWQGH (ORCPT ); Thu, 23 Sep 2021 12:06:07 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:35420 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242375AbhIWQFz (ORCPT ); Thu, 23 Sep 2021 12:05:55 -0400 Message-ID: <20210923153339.499688771@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1632413062; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=sbBPXL20B3WWl40L5vogsyQFErqzfiWcUOeM305JGdE=; b=jDe9+BmR+YJQYutVYfh3RwJdxUJQ6XmaSv4ZoSKtRszcqLvxDW9yuv0QSHdiRdR2QZKhfC OLn/LktqjcTv8L6lqkSORohdGs47GzCUCybyGxZkZm/U+nYblBlI8FDHdyhNigN9L4CWju Y8R3YdOb0Zvy26u/9oFA5+lr5DMJSMpQax3XbKszi2dXotKFXveLHfrwraP5gSLLtToJdf kDY9Jr3q+4nD/+UBWl+Wl/zIj7FSFsq5L29JEYKjgY6r/tcaE8SVLEv+LiY1cduIArUb1O dWcE/Ygmqx/HMpZvh2WoAEQwtBQkBmo8nLKDjjfGvls7aqaXGc6mApON+FmGPw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1632413062; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=sbBPXL20B3WWl40L5vogsyQFErqzfiWcUOeM305JGdE=; b=gW6FbrkvaIIfAks4rj5PIqn3U/pAOjMCyBnNM75IkMjxuy1E//zyY9mqSzH5ZAs2KWiqp5 X3SVq3/Qq3qYwJBA== From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Dmitry Vyukov , Johannes Berg Subject: [patch 02/11] mac80211-hwsim: Fix late beacon hrtimer handling References: <20210923153311.225307347@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Date: Thu, 23 Sep 2021 18:04:22 +0200 (CEST) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Johannes Berg Thomas explained in https://lore.kernel.org/r/87mtoeb4hb.ffs@tglx that our handling of the hrtimer here is wrong: If the timer fires late (e.g. due to vCPU scheduling, as reported by Dmitry/syzbot) then it tries to actually rearm the timer at the next deadline, which might be in the past already: 1 2 3 N N+1 | | | ... | | ^ intended to fire here (1) ^ next deadline here (2) ^ actually fired here The next time it fires, it's later, but will still try to schedule for the next deadline (now 3), etc. until it catches up with N, but that might take a long time, causing stalls etc. Now, all of this is simulation, so we just have to fix it, but note that the behaviour is wrong even per spec, since there's no value then in sending all those beacons unaligned - they should be aligned to the TBTT (1, 2, 3, ... in the picture), and if we're a bit (or a lot) late, then just resume at that point. Therefore, change the code to use hrtimer_forward_now() which will ensure that the next firing of the timer would be at N+1 (in the picture), i.e. the next interval point after the current time. Fixes: 01e59e467ecf ("mac80211_hwsim: hrtimer beacon") Reported-by: Dmitry Vyukov Reported-by: syzbot+0e964fad69a9c462bc1e@syzkaller.appspotmail.com Suggested-by: Thomas Gleixner Signed-off-by: Johannes Berg Signed-off-by: Thomas Gleixner Reviewed-by: Thomas Gleixner --- Note: This patch has already been applied in the wireless tree. It's just carried here for completeness sake so that the confinement of hrtimer_forward() in the last patch works. v2: add fixes tag - it's kind of old and the patch won't apply, but even the original hrtimer code here had this problem --- drivers/net/wireless/mac80211_hwsim.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/net/wireless/mac80211_hwsim.c b/drivers/net/wireless/mac80211_hwsim.c index ffa894f7312a..0adae76eb8df 100644 --- a/drivers/net/wireless/mac80211_hwsim.c +++ b/drivers/net/wireless/mac80211_hwsim.c @@ -1867,8 +1867,8 @@ mac80211_hwsim_beacon(struct hrtimer *timer) bcn_int -= data->bcn_delta; data->bcn_delta = 0; } - hrtimer_forward(&data->beacon_timer, hrtimer_get_expires(timer), - ns_to_ktime(bcn_int * NSEC_PER_USEC)); + hrtimer_forward_now(&data->beacon_timer, + ns_to_ktime(bcn_int * NSEC_PER_USEC)); return HRTIMER_RESTART; } -- 2.31.1