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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 123ECC43219 for ; Mon, 4 Oct 2021 13:15:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EFF5161B94 for ; Mon, 4 Oct 2021 13:15:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235832AbhJDNR0 (ORCPT ); Mon, 4 Oct 2021 09:17:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:55644 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235905AbhJDNP1 (ORCPT ); Mon, 4 Oct 2021 09:15:27 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3825961AAC; Mon, 4 Oct 2021 13:06:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1633352766; bh=RvA7bDhrihYWraeEEPp1LtI3X89eEYR+IOR0cbPg9+Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uqi9BpmpfxkkJOACWJ2T6ED3OO69vVNMvu0As+b/x6C/Qs1+eqcSTFNUJGPdbACNM Yc/Y0Vp3PJArHvblzQBdWbpgignHdJaqpVt0itOi+C6KVU8O+FSmG0ADZziU8WavUY JunT19goU/XASUhg8BN94AaKV1M+aIY+lCzFpGUA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Thomas Gleixner , Dmitry Vyukov , syzbot+0e964fad69a9c462bc1e@syzkaller.appspotmail.com, Johannes Berg , Sasha Levin Subject: [PATCH 5.4 18/56] mac80211-hwsim: fix late beacon hrtimer handling Date: Mon, 4 Oct 2021 14:52:38 +0200 Message-Id: <20211004125030.582583434@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20211004125030.002116402@linuxfoundation.org> References: <20211004125030.002116402@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Johannes Berg [ Upstream commit 313bbd1990b6ddfdaa7da098d0c56b098a833572 ] 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. Suggested-by: Thomas Gleixner Reported-by: Dmitry Vyukov Reported-by: syzbot+0e964fad69a9c462bc1e@syzkaller.appspotmail.com Fixes: 01e59e467ecf ("mac80211_hwsim: hrtimer beacon") Reviewed-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210915112936.544f383472eb.I3f9712009027aa09244b65399bf18bf482a8c4f1@changeid Signed-off-by: Johannes Berg Signed-off-by: Sasha Levin --- 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 1033513d3d9d..07b070b14d75 100644 --- a/drivers/net/wireless/mac80211_hwsim.c +++ b/drivers/net/wireless/mac80211_hwsim.c @@ -1603,8 +1603,8 @@ 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; } -- 2.33.0