From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932402AbdJZOX3 (ORCPT ); Thu, 26 Oct 2017 10:23:29 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:48116 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932234AbdJZOX0 (ORCPT ); Thu, 26 Oct 2017 10:23:26 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 6CD8E6034D Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=neeraju@codeaurora.org Subject: Re: Query regarding __hrtimer_get_next_event() To: Thomas Gleixner Cc: sramana@codeaurora.org, sboyd@codeaurora.org, LKML , John Stultz References: <2981b733-84ea-b46f-b16c-91aaa5a96c6c@codeaurora.org> From: Neeraj Upadhyay Message-ID: Date: Thu, 26 Oct 2017 19:53:22 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi tglx, Forgot to mention, we are using kernel stable version 3.18 https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/kernel/time/timekeeping.c?h=v3.18.77 wall time is being set to a value close to epoch but less than epoch + current uptime. Looks like https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/kernel/time?id=e1d7ba8735551ed79c7a0463a042353574b96da3 handles this case, but is not present in 3.18 tree. We will try by pulling this patch to 3.18 tree. int do_settimeofday(const struct timespec *tv) { xt = tk_xtime(tk); ts_delta.tv_sec = tv->tv_sec - xt.tv_sec; ts_delta.tv_nsec = tv->tv_nsec - xt.tv_nsec; tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta)); } xt = ( tv_sec = 1508807131, tv_nsec = 223767601) 2017/10/24 9:5:31 tk->wall_to_monotonic = ( tv_sec = -1508803094, tv_nsec = 15152092) ts_delta = (tv_sec = -1508803200, tv_nsec = -767601) wall_to_monotonic is bigger than the ts_delta, so leading to wall_to_monotonic become positive value, resulting in -ve off_real. Thanks Neeraj On 10/26/2017 06:27 PM, Thomas Gleixner wrote: > On Thu, 26 Oct 2017, Neeraj Upadhyay wrote: >> We have one query regarding the __hrtimer_get_next_event(). >> The expires_next.tv64 is set to 0 if it is < 0. We observed >> an hrtimer interrupt storm for one of the hrtimers with >> below properties: >> >> * Expires for the hrtimer was set to KTIME_MAX. >> * cpu base was HRTIMER_BASE_REALTIME with negative base->offset. >> * Due to below sub, expires overflowed to a negative value and >> expires_next.tv64 was set to 0 >> expires = ktime_sub(hrtimer_get_expires(timer), base->offset); >> * Due to this, clockevent was programmed to min_delta_ns, everytime >> as __hrtimer_get_next_event() returned 0. >> >> >> This may not be a valid use case (queuing a hrtimer with KTIME_MAX) >> expires, but should we guard the hrtimer next event code against >> this by using KTIME_MAX upper bound. Is something like below a >> proper way to guard it? Or am I missing something here? > Can you please explain how you managed to have a negative base->offset? > > Thanks, > > tglx -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation