From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 42F9E3446A7; Mon, 20 Apr 2026 16:10:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776701432; cv=none; b=mMMREfDQwDf0YxhZmLexsmYgKcBv/Ky8zgLHZ30oMeuRNpRvePRshJ74kzOADrgu1gVIWAIgt/NqdD6KrpvXAv13gZx43iaBG83yXazIn172C9CXAcy3Qzb+xoyJn8FJngGz2DJAKbakni9epu2+kXcFYWXMNcCx6ttyiVE6n9E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776701432; c=relaxed/simple; bh=Q2x3ZwJca8WJoXAe0I4LFpRqZi+9ENNoxtqFGQq+ikI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Lb5dLyxkhJNzdZsFdBSUFNuuDLkIm7H7UcU54bbBgxtJFCjCKnJLxalSRIq5A/vP4lzF/Z2e6UYLrjXcYBRUEvCehJK1wxVKkE0GrYwqAcrbIavt6H9O3nHLBaFaNXp80cT8V3JMjoIli13JHit1wePZ5ZEEFiX8LpMidNm/IXc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=nwv0GKzG; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="nwv0GKzG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CF212C19425; Mon, 20 Apr 2026 16:10:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776701432; bh=Q2x3ZwJca8WJoXAe0I4LFpRqZi+9ENNoxtqFGQq+ikI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nwv0GKzGw1MdNiFAgM3bUj4fwt1QiC10c+O5Kw6nkoFzHK8gep0v6JOjt5XhzuneL BwjArNm5/39Eo+Ywo1XmqQRTPNfJEzQitVdqbym0gqKRT1g4jbUpbczgQZV6uGccZn rMxDcumuJ8Lmy/X5GKNYnlvJGpMFzp11vhvWYYgI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Calvin Owens , Thomas Gleixner , Borislav Petkov , Sasha Levin Subject: [PATCH 6.12 084/162] clockevents: Prevent timer interrupt starvation Date: Mon, 20 Apr 2026 17:41:56 +0200 Message-ID: <20260420153930.076836934@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260420153927.006696811@linuxfoundation.org> References: <20260420153927.006696811@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner [ Upstream commit d6e152d905bdb1f32f9d99775e2f453350399a6a ] Calvin reported an odd NMI watchdog lockup which claims that the CPU locked up in user space. He provided a reproducer, which sets up a timerfd based timer and then rearms it in a loop with an absolute expiry time of 1ns. As the expiry time is in the past, the timer ends up as the first expiring timer in the per CPU hrtimer base and the clockevent device is programmed with the minimum delta value. If the machine is fast enough, this ends up in a endless loop of programming the delta value to the minimum value defined by the clock event device, before the timer interrupt can fire, which starves the interrupt and consequently triggers the lockup detector because the hrtimer callback of the lockup mechanism is never invoked. As a first step to prevent this, avoid reprogramming the clock event device when: - a forced minimum delta event is pending - the new expiry delta is less then or equal to the minimum delta Thanks to Calvin for providing the reproducer and to Borislav for testing and providing data from his Zen5 machine. The problem is not limited to Zen5, but depending on the underlying clock event device (e.g. TSC deadline timer on Intel) and the CPU speed not necessarily observable. This change serves only as the last resort and further changes will be made to prevent this scenario earlier in the call chain as far as possible. [ tglx: Updated to restore the old behaviour vs. !force and delta <= 0 and fixed up the tick-broadcast handlers as pointed out by Borislav ] Fixes: d316c57ff6bf ("[PATCH] clockevents: add core functionality") Reported-by: Calvin Owens Signed-off-by: Thomas Gleixner Tested-by: Calvin Owens Tested-by: Borislav Petkov Link: https://lore.kernel.org/lkml/acMe-QZUel-bBYUh@mozart.vkv.me/ Link: https://patch.msgid.link/20260407083247.562657657@kernel.org Signed-off-by: Sasha Levin --- include/linux/clockchips.h | 2 ++ kernel/time/clockevents.c | 27 +++++++++++++++++++-------- kernel/time/hrtimer.c | 1 + kernel/time/tick-broadcast.c | 8 +++++++- kernel/time/tick-common.c | 1 + kernel/time/tick-sched.c | 1 + 6 files changed, 31 insertions(+), 9 deletions(-) diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h index b0df28ddd394b..50cdc9da8d32a 100644 --- a/include/linux/clockchips.h +++ b/include/linux/clockchips.h @@ -80,6 +80,7 @@ enum clock_event_state { * @shift: nanoseconds to cycles divisor (power of two) * @state_use_accessors:current state of the device, assigned by the core code * @features: features + * @next_event_forced: True if the last programming was a forced event * @retries: number of forced programming retries * @set_state_periodic: switch state to periodic * @set_state_oneshot: switch state to oneshot @@ -108,6 +109,7 @@ struct clock_event_device { u32 shift; enum clock_event_state state_use_accessors; unsigned int features; + unsigned int next_event_forced; unsigned long retries; int (*set_state_periodic)(struct clock_event_device *); diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c index 78c7bd64d0ddf..6f4257e63bba8 100644 --- a/kernel/time/clockevents.c +++ b/kernel/time/clockevents.c @@ -172,6 +172,7 @@ void clockevents_shutdown(struct clock_event_device *dev) { clockevents_switch_state(dev, CLOCK_EVT_STATE_SHUTDOWN); dev->next_event = KTIME_MAX; + dev->next_event_forced = 0; } /** @@ -305,7 +306,6 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires, { unsigned long long clc; int64_t delta; - int rc; if (WARN_ON_ONCE(expires < 0)) return -ETIME; @@ -324,16 +324,27 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires, return dev->set_next_ktime(expires, dev); delta = ktime_to_ns(ktime_sub(expires, ktime_get())); - if (delta <= 0) - return force ? clockevents_program_min_delta(dev) : -ETIME; - delta = min(delta, (int64_t) dev->max_delta_ns); - delta = max(delta, (int64_t) dev->min_delta_ns); + /* Required for tick_periodic() during early boot */ + if (delta <= 0 && !force) + return -ETIME; + + if (delta > (int64_t)dev->min_delta_ns) { + delta = min(delta, (int64_t) dev->max_delta_ns); + clc = ((unsigned long long) delta * dev->mult) >> dev->shift; + if (!dev->set_next_event((unsigned long) clc, dev)) + return 0; + } - clc = ((unsigned long long) delta * dev->mult) >> dev->shift; - rc = dev->set_next_event((unsigned long) clc, dev); + if (dev->next_event_forced) + return 0; - return (rc && force) ? clockevents_program_min_delta(dev) : rc; + if (dev->set_next_event(dev->min_delta_ticks, dev)) { + if (!force || clockevents_program_min_delta(dev)) + return -ETIME; + } + dev->next_event_forced = 1; + return 0; } /* diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 640d2ea4bd1fa..7c57fe7d20d9a 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -1852,6 +1852,7 @@ void hrtimer_interrupt(struct clock_event_device *dev) BUG_ON(!cpu_base->hres_active); cpu_base->nr_events++; dev->next_event = KTIME_MAX; + dev->next_event_forced = 0; raw_spin_lock_irqsave(&cpu_base->lock, flags); entry_time = now = hrtimer_update_base(cpu_base); diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c index ed58eebb4e8f4..99d2978ef9b98 100644 --- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -76,8 +76,10 @@ const struct clock_event_device *tick_get_wakeup_device(int cpu) */ static void tick_broadcast_start_periodic(struct clock_event_device *bc) { - if (bc) + if (bc) { + bc->next_event_forced = 0; tick_setup_periodic(bc, 1); + } } /* @@ -403,6 +405,7 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev) bool bc_local; raw_spin_lock(&tick_broadcast_lock); + tick_broadcast_device.evtdev->next_event_forced = 0; /* Handle spurious interrupts gracefully */ if (clockevent_state_shutdown(tick_broadcast_device.evtdev)) { @@ -696,6 +699,7 @@ static void tick_handle_oneshot_broadcast(struct clock_event_device *dev) raw_spin_lock(&tick_broadcast_lock); dev->next_event = KTIME_MAX; + tick_broadcast_device.evtdev->next_event_forced = 0; next_event = KTIME_MAX; cpumask_clear(tmpmask); now = ktime_get(); @@ -1061,6 +1065,7 @@ static void tick_broadcast_setup_oneshot(struct clock_event_device *bc, bc->event_handler = tick_handle_oneshot_broadcast; + bc->next_event_forced = 0; bc->next_event = KTIME_MAX; /* @@ -1173,6 +1178,7 @@ void hotplug_cpu__broadcast_tick_pull(int deadcpu) } /* This moves the broadcast assignment to this CPU: */ + bc->next_event_forced = 0; clockevents_program_event(bc, bc->next_event, 1); } raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 9a3859443c042..4b5a42192afa2 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -110,6 +110,7 @@ void tick_handle_periodic(struct clock_event_device *dev) int cpu = smp_processor_id(); ktime_t next = dev->next_event; + dev->next_event_forced = 0; tick_periodic(cpu); /* diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index f203f000da1ad..e385555b456e8 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -1488,6 +1488,7 @@ static void tick_nohz_lowres_handler(struct clock_event_device *dev) struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); dev->next_event = KTIME_MAX; + dev->next_event_forced = 0; if (likely(tick_nohz_handler(&ts->sched_timer) == HRTIMER_RESTART)) tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); -- 2.53.0