From nobody Sun Feb 8 20:53:11 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C04B158229; Thu, 21 Mar 2024 11:24:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711020298; cv=none; b=kGfQ0pe+ZR6RE6qw4WR5XRgDfzOwzc6N+U37z/4RFgtdIwxsHHdstfYCkqQkISumPDjQPkyEKhQ3r4QJwSVjfUqzkrwDBvuz6I+qYW4Yg/Yi8GwdXHmQaYmGjgnmwmhOEXKdLS4KKmo1DOSCyIgVR3/5fa61mzufGIdpuNSOEko= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711020298; c=relaxed/simple; bh=gst+oXGb/4n8bIDsyLM0AG1Y3wMsVD9IZ4qrzg7eWkE=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=dxRzn2Xw1QD8+kCramEW5M0KC1XdwEJhQ/afSr1dbPsmUVhxQKSkku8lZznlm8Zw7JI3kmrg2r02OFBqyMprPmLOEqGlk+lMIBjnXAzfnVOYH5piYQNf9iBH0Y5l8sq4JJAWPLvz4GFNV2I3rlgLU+/LQtdlzxUXoU7Q9SZDavQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=QiDTb8t6; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=3jZnZioC; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="QiDTb8t6"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="3jZnZioC" Date: Thu, 21 Mar 2024 11:24:54 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1711020295; 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=gvgV9uRQ5mokoL+CWA1BFsXEAKiRYoaGZVn2rpFo8oc=; b=QiDTb8t6rcTwfdDayxmhLU6lL9U8sgtxRaFjC0bJI03zZXhylD0Aoz9lWyxGUM++S1iaRu 2MLBzF/8f10tsvk2Tv8R525fcGB4LUlQstbkd4g25QyHULBqXY8QunBTWEkLLzfLERd2KT 3L0hkQJ3Hni44TBkyfspO71DMxSs202JVNltQDSxhgMIHwbGQMyPDgs42QxRlga8T15lgb Za5ryDiAJjkQbX9AaO8b389M/Hy8Coo2tVLl26irNVkcEMWGz6Yfxo4cu4CobtAgfLXiF2 Uiht+/uuMQwe4No6NcdtNLMDTaB0RSLGfogcjU3qFYgDtSbarwR5Ew7QRMY3xA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1711020295; 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=gvgV9uRQ5mokoL+CWA1BFsXEAKiRYoaGZVn2rpFo8oc=; b=3jZnZioCScL1heQGmCqA89Lxn1TCLZ3x9/mJI1CRz+ade8upFhXqv0duESZHmHkYt4zQuB IwcQjPsGQfuK5eDg== From: "tip-bot2 for Frederic Weisbecker" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/urgent] timers/migration: Fix endless timer requeue after idle interrupts Cc: "Paul E. McKenney" , Frederic Weisbecker , Thomas Gleixner , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20240318230729.15497-2-frederic@kernel.org> References: <20240318230729.15497-2-frederic@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <171102029421.10875.6095806684976626047.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the timers/urgent branch of tip: Commit-ID: f55acb1e44f3d4bf1ca7926d777895a67d4ec606 Gitweb: https://git.kernel.org/tip/f55acb1e44f3d4bf1ca7926d777895a67= d4ec606 Author: Frederic Weisbecker AuthorDate: Tue, 19 Mar 2024 00:07:28 +01:00 Committer: Thomas Gleixner CommitterDate: Tue, 19 Mar 2024 10:14:55 +01:00 timers/migration: Fix endless timer requeue after idle interrupts When a CPU is an idle migrator, but another CPU wakes up before it, becomes an active migrator and handles the queue, the initial idle migrator may end up endlessly reprogramming its clockevent, chasing ghost timers forever such as in the following scenario: [GRP0:0] migrator =3D 0 active =3D 0 nextevt =3D T1 / \ 0 1 active idle (T1) 0) CPU 1 is idle and has a timer queued (T1), CPU 0 is active and is the active migrator. [GRP0:0] migrator =3D NONE active =3D NONE nextevt =3D T1 / \ 0 1 idle idle (T1) wakeup =3D T1 1) CPU 0 is now idle and is therefore the idle migrator. It has programmed its next timer interrupt to handle T1. [GRP0:0] migrator =3D 1 active =3D 1 nextevt =3D KTIME_MAX / \ 0 1 idle active wakeup =3D T1 2) CPU 1 has woken up, it is now active and it has just handled its own timer T1. 3) CPU 0 gets a timer interrupt to handle T1 but tmigr_handle_remote() realize it is not the migrator anymore. So it early returns without observing that T1 has been expired already and therefore without updating its ->wakeup value. 4) CPU 0 goes into tmigr_cpu_new_timer() which also early returns because it doesn't queue a timer of its own. So ->wakeup is left unchanged and the next timer is programmed to fire now. 5) goto 3) forever This results in timer interrupt storms in idle and also in nohz_full (as observed in rcutorture's TREE07 scenario). Fix this with forcing a re-evaluation of tmc->wakeup while trying remote timer handling when the CPU isn't the migrator anymmore. The check is inherently racy but in the worst case the CPU just races setting the KTIME_MAX value that a remote expiry also tries to set. Fixes: 7ee988770326 ("timers: Implement the hierarchical pull model") Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20240318230729.15497-2-frederic@kernel.org --- kernel/time/timer_migration.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c index 611cd90..c63a0af 100644 --- a/kernel/time/timer_migration.c +++ b/kernel/time/timer_migration.c @@ -1038,8 +1038,15 @@ void tmigr_handle_remote(void) * in tmigr_handle_remote_up() anyway. Keep this check to speed up the * return when nothing has to be done. */ - if (!tmigr_check_migrator(tmc->tmgroup, tmc->childmask)) - return; + if (!tmigr_check_migrator(tmc->tmgroup, tmc->childmask)) { + /* + * If this CPU was an idle migrator, make sure to clear its wakeup + * value so it won't chase timers that have already expired elsewhere. + * This avoids endless requeue from tmigr_new_timer(). + */ + if (READ_ONCE(tmc->wakeup) =3D=3D KTIME_MAX) + return; + } =20 data.now =3D get_jiffies_update(&data.basej);