From nobody Wed Feb 5 19:01:37 2025 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 25C1024A7F8; Thu, 16 Jan 2025 12:36:09 +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=1737030971; cv=none; b=fowlesvB+EfnPqyZilTJGcavK6ANb19T2AedbbsJkxXMZyQhJZoUkX+l2b54boVEkjtGLgqziGhnf4G6k5rxa1ajEjlM1qQ/x2zCpP8frIx1ZmDttl9y2nY8LcW7/bLIladxTMahHyaCRKtB3HXJSX5OPsksE8zKLbncryfFWuA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737030971; c=relaxed/simple; bh=Mc5NbTY5ITF1qqajCHYIWrEwVrAh6CQ+E20x2atM42Q=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=Rcu9ZPghgRBOE4A5RvKZOulC+pd1oObNybMnbfFdGor+cieDvs4KbtheCoDpjvAJF5Q9ejOWjUx+aCGVgGxRYU2bgSBbELJt+bXDojPuDtIRI0J1DsMt2bBfylVov4/80QA5LpTey20CV9xgsoainWVk2C1OwaBRY0IGX8P/2RE= 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=Ao2PcRIa; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=dDhuFC+8; 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="Ao2PcRIa"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="dDhuFC+8" Date: Thu, 16 Jan 2025 12:36:07 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1737030968; 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=Ej4l6wuZJB9G3BGGgBaL+wxiRkD0U0/BOuINWAZDAZo=; b=Ao2PcRIa/pm+SOXrXZNr4zZfzuCHTaxSeM0rHEmOJnSgp4Ope2c4CFbHeUCh6v3R1ybndL QP/Fb+tH3opQCwcpCwz222wrxUdxzGkGMzONxgVRhbDQzfE1f4FTJReAlhhF055O/+nchz JFhgYytl6MpYbVr0RLSafXB5/p0Xf60Oaif6NmEW16kmGxf2MF3iQxPx35lupZUGuUrzVN WON7WNm4ag+MrJN83D1AyO8I5r4Wy7ZCkz0KIWLGVauYAVNDqvdaDZmmcPiTateBr44UWV nGbPpKaKvozssAPNsHBMpwnMDkna72YgiFRymvH/24Q/ythwFQw9M9zxeeNJ2A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1737030968; 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=Ej4l6wuZJB9G3BGGgBaL+wxiRkD0U0/BOuINWAZDAZo=; b=dDhuFC+8tXj6TIscy8NUT5AhLmfgtWuN4xZarwzA5JAUPgnzU1J2kiK+r5CUM4+jqvKy3l av4VbCPtDWZTG6BA== From: "tip-bot2 for Koichiro Den" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/urgent] hrtimers: Handle CPU state correctly on hotplug Cc: Koichiro Den , Thomas Gleixner , stable@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20241220134421.3809834-1-koichiro.den@canonical.com> References: <20241220134421.3809834-1-koichiro.den@canonical.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <173703096711.31546.10185525717139575022.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: 2f8dea1692eef2b7ba6a256246ed82c365fdc686 Gitweb: https://git.kernel.org/tip/2f8dea1692eef2b7ba6a256246ed82c36= 5fdc686 Author: Koichiro Den AuthorDate: Fri, 20 Dec 2024 22:44:21 +09:00 Committer: Thomas Gleixner CommitterDate: Thu, 16 Jan 2025 13:06:14 +01:00 hrtimers: Handle CPU state correctly on hotplug Consider a scenario where a CPU transitions from CPUHP_ONLINE to halfway through a CPU hotunplug down to CPUHP_HRTIMERS_PREPARE, and then back to CPUHP_ONLINE: Since hrtimers_prepare_cpu() does not run, cpu_base.hres_active remains set to 1 throughout. However, during a CPU unplug operation, the tick and the clockevents are shut down at CPUHP_AP_TICK_DYING. On return to the online state, for instance CFS incorrectly assumes that the hrtick is already active, and the chance of the clockevent device to transition to oneshot mode is also lost forever for the CPU, unless it goes back to a lower state than CPUHP_HRTIMERS_PREPARE once. This round-trip reveals another issue; cpu_base.online is not set to 1 after the transition, which appears as a WARN_ON_ONCE in enqueue_hrtimer(). Aside of that, the bulk of the per CPU state is not reset either, which means there are dangling pointers in the worst case. Address this by adding a corresponding startup() callback, which resets the stale per CPU state and sets the online flag. [ tglx: Make the new callback unconditionally available, remove the online modification in the prepare() callback and clear the remaining state in the starting callback instead of the prepare callback ] Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CP= U earlier") Signed-off-by: Koichiro Den Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20241220134421.3809834-1-koichiro.den@can= onical.com --- include/linux/hrtimer.h | 1 + kernel/cpu.c | 2 +- kernel/time/hrtimer.c | 11 ++++++++++- 3 files changed, 12 insertions(+), 2 deletions(-) diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h index 7ef5f7e..f7bfdcf 100644 --- a/include/linux/hrtimer.h +++ b/include/linux/hrtimer.h @@ -386,6 +386,7 @@ extern void __init hrtimers_init(void); extern void sysrq_timer_list_show(void); =20 int hrtimers_prepare_cpu(unsigned int cpu); +int hrtimers_cpu_starting(unsigned int cpu); #ifdef CONFIG_HOTPLUG_CPU int hrtimers_cpu_dying(unsigned int cpu); #else diff --git a/kernel/cpu.c b/kernel/cpu.c index b605334..0509a97 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2179,7 +2179,7 @@ static struct cpuhp_step cpuhp_hp_states[] =3D { }, [CPUHP_AP_HRTIMERS_DYING] =3D { .name =3D "hrtimers:dying", - .startup.single =3D NULL, + .startup.single =3D hrtimers_cpu_starting, .teardown.single =3D hrtimers_cpu_dying, }, [CPUHP_AP_TICK_DYING] =3D { diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 80fe374..030426c 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -2202,6 +2202,15 @@ int hrtimers_prepare_cpu(unsigned int cpu) } =20 cpu_base->cpu =3D cpu; + hrtimer_cpu_base_init_expiry_lock(cpu_base); + return 0; +} + +int hrtimers_cpu_starting(unsigned int cpu) +{ + struct hrtimer_cpu_base *cpu_base =3D this_cpu_ptr(&hrtimer_bases); + + /* Clear out any left over state from a CPU down operation */ cpu_base->active_bases =3D 0; cpu_base->hres_active =3D 0; cpu_base->hang_detected =3D 0; @@ -2210,7 +2219,6 @@ int hrtimers_prepare_cpu(unsigned int cpu) cpu_base->expires_next =3D KTIME_MAX; cpu_base->softirq_expires_next =3D KTIME_MAX; cpu_base->online =3D 1; - hrtimer_cpu_base_init_expiry_lock(cpu_base); return 0; } =20 @@ -2286,5 +2294,6 @@ int hrtimers_cpu_dying(unsigned int dying_cpu) void __init hrtimers_init(void) { hrtimers_prepare_cpu(smp_processor_id()); + hrtimers_cpu_starting(smp_processor_id()); open_softirq(HRTIMER_SOFTIRQ, hrtimer_run_softirq); }