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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D60DC77B7A for ; Thu, 1 Jun 2023 13:22:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233537AbjFANWY (ORCPT ); Thu, 1 Jun 2023 09:22:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59134 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233486AbjFANWN (ORCPT ); Thu, 1 Jun 2023 09:22:13 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 056AB19B for ; Thu, 1 Jun 2023 06:22:04 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3295664435 for ; Thu, 1 Jun 2023 13:21:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 433D0C433D2; Thu, 1 Jun 2023 13:21:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1685625718; bh=wU8Vu9bgI8KbbN4ljQAHM+Omu6PSOvAFrS2vgPhZtVw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gIj9aps68UB3wq/gUpFKTAq6Fog98L16LqkWWzpaCfmsmXEmZ2fAjHUNVlVtFR7Gd VQZ7LfKlzo5aSM1DMHU5aCfO+4gPJGZ2xcEBC/8DdEB1WI3B6Lw0xOUHmgyHklqDJs hC6TiIh3usXktKu4OtiWf2jbEvkVZnZQWdKgWlchCJwYweVrNysZpVAqrlzKmzzwls 5iVUh+cPkytdH7mQewvgqxVIhHQSJlMD4hFDGS4z71z24R/Aoyv2qI/I5unewdUb4R hYGR2EF2Lu/1HnXqpBMX8LQxx/DpJBFXISaUYcyJIM6lL/zqGKMxwPRZDw4xR9zXpc ifz+UzUVzg1GA== Date: Thu, 1 Jun 2023 15:21:55 +0200 From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , Anna-Maria Behnsen , Peter Zijlstra , Sebastian Siewior , syzbot+5c54bd3eb218bb595aa9@syzkaller.appspotmail.com, Dmitry Vyukov , Michael Kerrisk Subject: Re: [patch 18/20] posix-timers: Clarify posix_timer_fn() comments Message-ID: References: <20230425181827.219128101@linutronix.de> <20230425183313.777610259@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230425183313.777610259@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 25, 2023 at 08:49:24PM +0200, Thomas Gleixner wrote: > Make the issues vs. SIG_IGN understandable and remove the 15 years old > promise that a proper solution is already on the horizon. > > Signed-off-by: Thomas Gleixner > --- > kernel/time/posix-timers.c | 56 +++++++++++++++++++++------------------------ > 1 file changed, 27 insertions(+), 29 deletions(-) > > --- a/kernel/time/posix-timers.c > +++ b/kernel/time/posix-timers.c > @@ -325,11 +325,11 @@ int posix_timer_event(struct k_itimer *t > } > > /* > - * This function gets called when a POSIX.1b interval timer expires. It > - * is used as a callback from the kernel internal timer. The > - * run_timer_list code ALWAYS calls with interrupts on. > - > - * This code is for CLOCK_REALTIME* and CLOCK_MONOTONIC* timers. > + * This function gets called when a POSIX.1b interval timer expires from > + * the HRTIMER soft interrupt with interrupts enabled. BTW, what arranges for this to be called in softirq with interrupts enabled? The modes I see used here are HRTIMER_MODE_ABS or HRTIMER_MODE_REL and not their _SOFT counterparts. > + * > + * Handles CLOCK_REALTIME, CLOCK_MONOTONIC, CLOCK_BOOTTIME and CLOCK_TAI > + * based timers. > */ > static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer) > { > @@ -358,34 +359,31 @@ static enum hrtimer_restart posix_timer_ > * FIXME: What we really want, is to stop this > * timer completely and restart it in case the > * SIG_IGN is removed. This is a non trivial > - * change which involves sighand locking > - * (sigh !), which we don't want to do late in > - * the release cycle. > + * change to the signal handling code. > + * > + * For now let timers with an interval less than a > + * jiffie expire every jiffie to avoid softirq Or rather at least to the next jiffie, right? Because then in the next jiffie it gets re-evaluated in case a real signal handler might have been set in-between. Or it could be: + * For now let timers with an interval less than a + * jiffie expire every jiffie (until a real sig handler + * is found set) to avoid softirq... > + * starvation in case of SIG_IGN and a very small > + * interval, which would put the timer right back > + * on the softirq pending list. Moving now ahead of > + * time tricks hrtimer_forward() to expire the > + * timer later, while it still maintains the > + * overrun accuracy for the price of a slightly > + * inconsistency in the timer_gettime() case. This > + * is at least better than a starved softirq. [...] > */ > -#ifdef CONFIG_HIGH_RES_TIMERS > - { > + if (IS_ENABLED(CONFIG_HIGHRES_TIMERS)) { > ktime_t kj = NSEC_PER_SEC / HZ; Could be TICK_NSECS? Thanks! > > if (timr->it_interval < kj) > now = ktime_add(now, kj); > } > -#endif > - timr->it_overrun += hrtimer_forward(timer, now, > - timr->it_interval); > + > + timr->it_overrun += hrtimer_forward(timer, now, timr->it_interval); > ret = HRTIMER_RESTART; > ++timr->it_requeue_pending; > timr->it_active = 1; >