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=-3.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 EF9F3C433E0 for ; Thu, 9 Jul 2020 09:42:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C2C3E206E2 for ; Thu, 9 Jul 2020 09:42:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="KAnYRExa"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="NyOsSDHs" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726538AbgGIJmn (ORCPT ); Thu, 9 Jul 2020 05:42:43 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:35504 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726340AbgGIJmn (ORCPT ); Thu, 9 Jul 2020 05:42:43 -0400 Date: Thu, 9 Jul 2020 11:42:31 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1594287761; 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: in-reply-to:in-reply-to:references:references; bh=Tv8JpSeZXcMnPyOcvS3LIZo/plB16DDrs7eh/Dbn2NE=; b=KAnYRExauboyU3r6nTaiA/r+xYLp+5YXkBeQ6qAyAl/CfngMpXl8i/suBI2W1TnN4C+oPQ hwjqvrBo61PRvB9YuWDwA/P7sBWYmFwJa9+9UIheZyOuHWouJVCuPpBcy1L3HgKU81pxDW kRxcpwkLcWk/G5ijbjPOhfikwxUQv2QyWOWUkjNQDbgSMw1JW9mEwzA8V+U05WsK9FLnsg LpPzveqn+AKdSqR6PJHqLt5SpfQ59BLDWB6xprJnR1TSV2YtjqGXTrxLeVkq8n8q43/fUh 4+Dsy7vmAR/P/Fjfzq2UIaMf5hfIviKQAosFA+c21Tabkt/+0tdSTM26g/AJ9g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1594287761; 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: in-reply-to:in-reply-to:references:references; bh=Tv8JpSeZXcMnPyOcvS3LIZo/plB16DDrs7eh/Dbn2NE=; b=NyOsSDHsWGfbfMDjtlixUGbS4/NFLx5p726DirUgeE+QrxamOrBPPRsgwN2OpupZ8jUgR3 cz53UMlgUcvPV+BQ== From: Anna-Maria Behnsen To: Frederic Weisbecker cc: Thomas Gleixner , LKML , Peter Zijlstra , Juri Lelli , Stable Subject: Re: [PATCH] timer: Prevent base->clk from moving backward In-Reply-To: <20200703010657.2302-1-frederic@kernel.org> Message-ID: References: <20200703010657.2302-1-frederic@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Fri, 3 Jul 2020, Frederic Weisbecker wrote: > When a timer is enqueued with a negative delta (ie: expiry is below > base->clk), it gets added to the wheel as expiring now (base->clk). > > Yet the value that gets stored in base->next_expiry, while calling > trigger_dyntick_cpu(), is the initial timer->expires value. The > resulting state becomes: > > base->next_expiry < base->clk > > On the next timer enqueue, forward_timer_base() may accidentally > rewind base->clk. As a possible outcome, timers may expire way too > early, the worst case being that the highest wheel levels get spuriously > processed again. > > To prevent from that, make sure that base->next_expiry doesn't get below > base->clk. > > Fixes: a683f390b93f ("timers: Forward the wheel clock whenever possible") > Signed-off-by: Frederic Weisbecker > Cc: Peter Zijlstra > Cc: Anna-Maria Gleixner > Cc: Juri Lelli > --- Reviewed-by: Anna-Maria Behnsen Thanks, Anna-Maria