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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 0BB1DC3A5A0 for ; Mon, 19 Aug 2019 15:27:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C423722CE2 for ; Mon, 19 Aug 2019 15:27:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="bL8Rajdz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727193AbfHSP1D (ORCPT ); Mon, 19 Aug 2019 11:27:03 -0400 Received: from mail-lj1-f196.google.com ([209.85.208.196]:45380 "EHLO mail-lj1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726390AbfHSP1D (ORCPT ); Mon, 19 Aug 2019 11:27:03 -0400 Received: by mail-lj1-f196.google.com with SMTP id l1so2143241lji.12; Mon, 19 Aug 2019 08:27:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mzhnd/NgWWbF1n6qQYdEPf3DMaCqwz6w2KWcI54F4xw=; b=bL8RajdzINCDTNJd556aiA1a1hywhD2wofkFUBlK2ey0iTsL4vJoq7v2htihsXCBOp H7IchW2FiKTPe+DY711s23VkPXxwU06x6G5+WDNI9kaNYj3dbQXzPnEgg3mXOaA2sN5T 60OpvNb3hLEb4BKgpn65PVOxEniZKrTsxvgRmmWzyc4kvGATsolcEUAX3MQDWmnT3GoZ vlLBZoc2Oe3MwXz3t2tc0ITUJmNucxOr992TZvJoSIlKfUrBmx1/ajsfXKc/qt1JfJqM 3SrIikXcP4W4dqnlqEvsCcjfNvTHfvxf75DZiybW3HAIQ7b2HfkNdIXgtJghIYiiqWxH i9qg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mzhnd/NgWWbF1n6qQYdEPf3DMaCqwz6w2KWcI54F4xw=; b=PTzzfm7fRCauJBRA9YQsali0dvm/eGZYQemwLpx6RWjmwQSggaEHQCWjttliPvpaIV 9lGND5vTLt00nNC3vU9kvn9w7J46YpenMrUzhvikzyz3sopfqfdg1WoiCk52nLSN2RPD klT7chzB0e8MlilnpoBedGzST8ZIt3bJi4TpP22a5QbHQNpHeL5MB9FrAS5r6yB+T/AJ KJostnhTZdwOA9d42dGUwFVfiB8W7i58aPgLUcA2emGkFURowCe/0n/GnR0181aDTacM RA0Vh1HPaLRL2o6YCdmuBragDIHUpWdtFKbabzdj0oAk17/UDW6LN/hWYVyserFCDTyD RlvQ== X-Gm-Message-State: APjAAAXNf0magj5JDwhiW9prDotzz1rOgXJkZjdWOc3bE5r0u83cmLDn 1X7Ci9EuJ8d9yRdhO0AZqlGpT5LS4Jks+MWYqS5ZGamL X-Google-Smtp-Source: APXvYqxqV1P8WjGmVBMQPRR8Ea2ssckOGKhnvRYGTuez+x5pJMX7rPhFgc/NSjCMts8zP+KcL4SCg/V3HKEmiBFqOvc= X-Received: by 2002:a2e:4601:: with SMTP id t1mr1402539lja.102.1566228421044; Mon, 19 Aug 2019 08:27:01 -0700 (PDT) MIME-Version: 1.0 References: <20190816083246.169312-1-arul.jeniston@gmail.com> In-Reply-To: From: Arul Jeniston Date: Mon, 19 Aug 2019 20:56:49 +0530 Message-ID: Subject: Re: [PATCH] FS: timerfd: Fix unexpected return value of timerfd_read function. To: Thomas Gleixner Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, arul_mc@dell.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org hi Tglx, > But for the above scenario: > > ktime_get() > do { > seq = read_seqcount_begin(&tk_core.seq); > base = tk->tkr_mono.base; > nsecs = timekeeping_get_ns(&tk->tkr_mono); > > } while (read_seqcount_retry(&tk_core.seq, seq)); > > So if the interrupt which updates the timekeeper hits in the middle of > timekeeping_get_ns() then the result is discarded because the sequence > count changed and read_seqcount_retry() returns true. So it takes another > round which will be perfectly aligned with the updated time keeper. > Do you mean to say the timekeeper updates always happen from ktime_get? My point was, when one thread is in ktime_get other thread/isr updates timekeeper from different flow. Regards, Arul