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 55542C7EE3A for ; Mon, 5 Jun 2023 15:09:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234275AbjFEPJZ (ORCPT ); Mon, 5 Jun 2023 11:09:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234231AbjFEPIe (ORCPT ); Mon, 5 Jun 2023 11:08:34 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59780F1; Mon, 5 Jun 2023 08:08:33 -0700 (PDT) Date: Mon, 05 Jun 2023 15:08:31 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1685977711; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=if2dVjYa5Bi/ydn9IhPeAQMayijHDMtDpj3hYChXRrM=; b=3V9VYLj+6bPxodnXQaHdrFFS1L2pA2xBGBUlnifBtNBdlVEd6L3Q3upqiOOc22u6UgW8xw nqhoZJuo3iEj82TpsrYHFbkKPFwtNYI6FOjmlYTfq4OHMAuFUx5joR1mZ0izXYGHoYYfEE ViBDZJ+dlhwLEazUHDkQUp7EzaOtPCfkP8MX7EC9QvYL0LZ9d+t/yMocKpJCXwAN441IfP xGxL6CEKe1EjY7TKMyriHl2xFJA/V7gF/GTS1LJoMolQtRdSY6AS7TXTZK7xuGdVpOzpCS W8/qRNGBgI1wSHkCdpGuiZZOd1NDoUDVfMWwddWKp8mLnWyOBfA2/u8hKGOEVA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1685977711; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=if2dVjYa5Bi/ydn9IhPeAQMayijHDMtDpj3hYChXRrM=; b=QEr+VH/c5GfbB0LGGQXy4t2GAp43L2wpyw5CwdXMnijOCP921O73PvP6WuIq6Dey50yXqw KadpD0q/VdcMdwAQ== From: "tip-bot2 for Thomas Gleixner" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/core] posix-timers: Clarify timer_wait_running() comment Cc: Thomas Gleixner , Frederic Weisbecker , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230425183312.985681995@linutronix.de> References: <20230425183312.985681995@linutronix.de> MIME-Version: 1.0 Message-ID: <168597771152.404.15026662809779436776.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the timers/core branch of tip: Commit-ID: 07ca14d623d8b0e6c4a0d3de4ca8a8ea35a85470 Gitweb: https://git.kernel.org/tip/07ca14d623d8b0e6c4a0d3de4ca8a8ea35a85470 Author: Thomas Gleixner AuthorDate: Tue, 25 Apr 2023 20:49:00 +02:00 Committer: Thomas Gleixner CommitterDate: Mon, 05 Jun 2023 17:03:37 +02:00 posix-timers: Clarify timer_wait_running() comment Explain it better and add the CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y aspect for completeness. Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lore.kernel.org/r/20230425183312.985681995@linutronix.de --- kernel/time/posix-timers.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 2c5daeb..4017533 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -836,10 +836,18 @@ static void common_timer_wait_running(struct k_itimer *timer) } /* - * On PREEMPT_RT this prevent priority inversion against softirq kthread in - * case it gets preempted while executing a timer callback. See comments in - * hrtimer_cancel_wait_running. For PREEMPT_RT=n this just results in a - * cpu_relax(). + * On PREEMPT_RT this prevents priority inversion and a potential livelock + * against the ksoftirqd thread in case that ksoftirqd gets preempted while + * executing a hrtimer callback. + * + * See the comments in hrtimer_cancel_wait_running(). For PREEMPT_RT=n this + * just results in a cpu_relax(). + * + * For POSIX CPU timers with CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n this is + * just a cpu_relax(). With CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y this + * prevents spinning on an eventually scheduled out task and a livelock + * when the task which tries to delete or disarm the timer has preempted + * the task which runs the expiry in task work context. */ static struct k_itimer *timer_wait_running(struct k_itimer *timer, unsigned long *flags)