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[2620:137:e000::1:20]) by mx.google.com with ESMTP id ij6-20020a170902ab4600b0019cc4426180si14120653plb.240.2023.04.25.11.50.21; Tue, 25 Apr 2023 11:50:36 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b=YFqFZlAf; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234732AbjDYStR (ORCPT + 99 others); Tue, 25 Apr 2023 14:49:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234688AbjDYStI (ORCPT ); Tue, 25 Apr 2023 14:49:08 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 189AD16F3D for ; Tue, 25 Apr 2023 11:49:02 -0700 (PDT) Message-ID: <20230425183312.985681995@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1682448540; 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: references:references; bh=q6yQSMh5NftPeZgPAUvdDD7ZWt6JAf5f2/3w3UhJ70Q=; b=YFqFZlAfXnLvCdWhP63tL7EqJG01euEvWnXMKyZ4fWLintzWYtQlDrz4x1F3Le+A34Eu/S bEX9uXMigiFk+vTmiWsSTAgJVTghexsnMwawy/0Bx6Dy4xKuxOtZJvZXnCILC7l25yb3Up 903ETpG3x3NpT6Cc8ue9GhAyXo1/CWzJVI3eup3kQucU0TYY5qxUwcMl8+h5omMXk0ToOp OoPbtFqFebZWIzfMIlGAtYbdsA7NEglKqS563SzLDghA/a3CTk1B/NEuqFl+Q+YykxsmJq TU+ouYWxJ7GEP6381AnkoR6Lk5W41pEU0kDLQAwW9YZyrXsZFpGV5WYxmrOgog== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1682448540; 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: references:references; bh=q6yQSMh5NftPeZgPAUvdDD7ZWt6JAf5f2/3w3UhJ70Q=; b=mDOvRu4hOE3asu9/pisMKyXQeVXK2GPXNrCGQlnPFD3m0O4j1dO4Z5wx4QztID7kjjCE6/ K7mtYEnp2qE3OrAQ== From: Thomas Gleixner To: LKML Cc: Frederic Weisbecker , Anna-Maria Behnsen , Peter Zijlstra , Sebastian Siewior , syzbot+5c54bd3eb218bb595aa9@syzkaller.appspotmail.com, Dmitry Vyukov , Michael Kerrisk Subject: [patch 03/20] posix-timers: Clarify timer_wait_running() comment References: <20230425181827.219128101@linutronix.de> MIME-Version: 1.0 Date: Tue, 25 Apr 2023 20:49:00 +0200 (CEST) X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1764175261657431559?= X-GMAIL-MSGID: =?utf-8?q?1764175261657431559?= 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 --- kernel/time/posix-timers.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -835,10 +835,18 @@ static void common_timer_wait_running(st } /* - * 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)