From nobody Sun Feb 8 12:51:43 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 D4D2F1547CA; Fri, 7 Feb 2025 08:13:14 +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=1738915996; cv=none; b=qkolyYY1MJOgK4oHXwqQ53HmvXtPSxliZ73k+9ZrWa4lDCWNSA4b20vTsGAlSCuXx2XP8rtoFazyti3+gZkzyFTNGwdVIOF+7Ps8rck1BX6x/fS6Obh3ViuQfdhJ+kO3nDYYJO9DJNjrly6RGEN8y42pFuaJgzC8wGD15befDW4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738915996; c=relaxed/simple; bh=pwdgnneK3dst1VUutsdE5GPzlHdvaje/IbI+REn1fKg=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=TiaAxFx9lu4kSclDakCdQ32ngLcUWN0+9Rig8kGy8uQUXsvutXUWzwOfSDoXSOQxvGDVK/9NXl8VUD3icZvxbXzvaEHRKYf1lxe9C1rtFi+faKs0XaWznOEV/j296XgzVb1bOmFecrEwmebwlMUcRgORpU5ln8SNsRdiORRcfLo= 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=36MBkKWr; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=bw1eyIbx; 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="36MBkKWr"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="bw1eyIbx" Date: Fri, 07 Feb 2025 08:13:12 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1738915993; 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=qZjbsWaHjvehxwqwuNv4yk95BFAXowqdx+sHrdVqZDY=; b=36MBkKWrrNXZVJ4U2quYSC+nC3cyy2oRnVm7Mirx+l3rNwxRmTM1haBc5m/MJgly88Uw6H 3M1GsI/xxhzYiMhKXfDMNml5/0pI5cslPTobTIV4b/1jG9ju4JBdwGIU+abOHm8tDyLJqG /ZwSpzuss9NWLlmYhwf3rDDF3Qib82As94qd7vUFto7s4XuKJclXjIosuBClNpiAMNP+R2 eY8wAhwU0ckJArtwAsANjL+Sh7REVg8xYkVsrqXTSwnhkgFwC1gzVwO0wu25lW4L7areJT qCZ7sKEZiDoQ96vGLZZml+evQ9dzfWHO0jju/JaBnwxpQumTNeu0NzHFOevyeA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1738915993; 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=qZjbsWaHjvehxwqwuNv4yk95BFAXowqdx+sHrdVqZDY=; b=bw1eyIbxNJF2KrqmA9sJlfM+RQVZ2R8+4bhaN4yK8xak+/vCmCG27v2gBeSaXOH0R16E6t clthY5R0Qz7yvwAA== 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 off-by-one root mis-connection Cc: Matt Fleming , Frederic Weisbecker , Thomas Gleixner , stable@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20250205160220.39467-1-frederic@kernel.org> References: <20250205160220.39467-1-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: <173891599227.10177.12341111504955542995.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: 868c9037df626b3c245ee26a290a03ae1f9f58d3 Gitweb: https://git.kernel.org/tip/868c9037df626b3c245ee26a290a03ae1= f9f58d3 Author: Frederic Weisbecker AuthorDate: Wed, 05 Feb 2025 17:02:20 +01:00 Committer: Thomas Gleixner CommitterDate: Fri, 07 Feb 2025 09:02:16 +01:00 timers/migration: Fix off-by-one root mis-connection Before attaching a new root to the old root, the children counter of the new root is checked to verify that only the upcoming CPU's top group have been connected to it. However since the recently added commit b729cc1ec21a ("timers/migration: Fix another race between hotplug and idle entry/exit") this check is not valid anymore because the old root is pre-accounted as a child to the new root. Therefore after connecting the upcoming CPU's top group to the new root, the children count to be expected must be 2 and not 1 anymore. This omission results in the old root to not be connected to the new root. Then eventually the system may run with more than one top level, which defeats the purpose of a single idle migrator. Also the old root is pre-accounted but not connected upon the new root creation. But it can be connected to the new root later on. Therefore the old root may be accounted twice to the new root. The propagation of such overcommit can end up creating a double final top-level root with a groupmask incorrectly initialized. Although harmless given that the final top level roots will never have a parent to walk up to, this oddity opportunistically reported the core issue: WARNING: CPU: 8 PID: 0 at kernel/time/timer_migration.c:543 tmigr_require= s_handle_remote CPU: 8 UID: 0 PID: 0 Comm: swapper/8 RIP: 0010:tmigr_requires_handle_remote Call Trace: ? tmigr_requires_handle_remote ? hrtimer_run_queues update_process_times tick_periodic tick_handle_periodic __sysvec_apic_timer_interrupt sysvec_apic_timer_interrupt Fix the problem by taking the old root into account in the children count of the new root so the connection is not omitted. Also warn when more than one top level group exists to better detect similar issues in the future. Fixes: b729cc1ec21a ("timers/migration: Fix another race between hotplug an= d idle entry/exit") Reported-by: Matt Fleming Signed-off-by: Frederic Weisbecker Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20250205160220.39467-1-frederic@kernel.org --- kernel/time/timer_migration.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c index 9cb9b65..2f63308 100644 --- a/kernel/time/timer_migration.c +++ b/kernel/time/timer_migration.c @@ -1675,6 +1675,9 @@ static int tmigr_setup_groups(unsigned int cpu, unsig= ned int node) =20 } while (i < tmigr_hierarchy_levels); =20 + /* Assert single root */ + WARN_ON_ONCE(!err && !group->parent && !list_is_singular(&tmigr_level_lis= t[top])); + while (i > 0) { group =3D stack[--i]; =20 @@ -1716,7 +1719,12 @@ static int tmigr_setup_groups(unsigned int cpu, unsi= gned int node) WARN_ON_ONCE(top =3D=3D 0); =20 lvllist =3D &tmigr_level_list[top]; - if (group->num_children =3D=3D 1 && list_is_singular(lvllist)) { + + /* + * Newly created root level should have accounted the upcoming + * CPU's child group and pre-accounted the old root. + */ + if (group->num_children =3D=3D 2 && list_is_singular(lvllist)) { /* * The target CPU must never do the prepare work, except * on early boot when the boot CPU is the target. Otherwise