From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- drivers/rtc/rtc-m48t35.c | 193 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 193 insertions(+) create mode 100644 drivers/rtc/rtc-m48t35.c (limited to 'drivers/rtc/rtc-m48t35.c') diff --git a/drivers/rtc/rtc-m48t35.c b/drivers/rtc/rtc-m48t35.c new file mode 100644 index 000000000..92f19bf99 --- /dev/null +++ b/drivers/rtc/rtc-m48t35.c @@ -0,0 +1,193 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Driver for the SGS-Thomson M48T35 Timekeeper RAM chip + * + * Copyright (C) 2000 Silicon Graphics, Inc. + * Written by Ulf Carlsson (ulfc@engr.sgi.com) + * + * Copyright (C) 2008 Thomas Bogendoerfer + * + * Based on code written by Paul Gortmaker. + */ + +#include +#include +#include +#include +#include +#include +#include + +struct m48t35_rtc { + u8 pad[0x7ff8]; /* starts at 0x7ff8 */ +#ifdef CONFIG_SGI_IP27 + u8 hour; + u8 min; + u8 sec; + u8 control; + u8 year; + u8 month; + u8 date; + u8 day; +#else + u8 control; + u8 sec; + u8 min; + u8 hour; + u8 day; + u8 date; + u8 month; + u8 year; +#endif +}; + +#define M48T35_RTC_SET 0x80 +#define M48T35_RTC_READ 0x40 + +struct m48t35_priv { + struct rtc_device *rtc; + struct m48t35_rtc __iomem *reg; + size_t size; + unsigned long baseaddr; + spinlock_t lock; +}; + +static int m48t35_read_time(struct device *dev, struct rtc_time *tm) +{ + struct m48t35_priv *priv = dev_get_drvdata(dev); + u8 control; + + /* + * Only the values that we read from the RTC are set. We leave + * tm_wday, tm_yday and tm_isdst untouched. Even though the + * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated + * by the RTC when initially set to a non-zero value. + */ + spin_lock_irq(&priv->lock); + control = readb(&priv->reg->control); + writeb(control | M48T35_RTC_READ, &priv->reg->control); + tm->tm_sec = readb(&priv->reg->sec); + tm->tm_min = readb(&priv->reg->min); + tm->tm_hour = readb(&priv->reg->hour); + tm->tm_mday = readb(&priv->reg->date); + tm->tm_mon = readb(&priv->reg->month); + tm->tm_year = readb(&priv->reg->year); + writeb(control, &priv->reg->control); + spin_unlock_irq(&priv->lock); + + tm->tm_sec = bcd2bin(tm->tm_sec); + tm->tm_min = bcd2bin(tm->tm_min); + tm->tm_hour = bcd2bin(tm->tm_hour); + tm->tm_mday = bcd2bin(tm->tm_mday); + tm->tm_mon = bcd2bin(tm->tm_mon); + tm->tm_year = bcd2bin(tm->tm_year); + + /* + * Account for differences between how the RTC uses the values + * and how they are defined in a struct rtc_time; + */ + tm->tm_year += 70; + if (tm->tm_year <= 69) + tm->tm_year += 100; + + tm->tm_mon--; + return 0; +} + +static int m48t35_set_time(struct device *dev, struct rtc_time *tm) +{ + struct m48t35_priv *priv = dev_get_drvdata(dev); + unsigned char mon, day, hrs, min, sec; + unsigned int yrs; + u8 control; + + yrs = tm->tm_year + 1900; + mon = tm->tm_mon + 1; /* tm_mon starts at zero */ + day = tm->tm_mday; + hrs = tm->tm_hour; + min = tm->tm_min; + sec = tm->tm_sec; + + if (yrs < 1970) + return -EINVAL; + + yrs -= 1970; + if (yrs > 255) /* They are unsigned */ + return -EINVAL; + + if (yrs > 169) + return -EINVAL; + + if (yrs >= 100) + yrs -= 100; + + sec = bin2bcd(sec); + min = bin2bcd(min); + hrs = bin2bcd(hrs); + day = bin2bcd(day); + mon = bin2bcd(mon); + yrs = bin2bcd(yrs); + + spin_lock_irq(&priv->lock); + control = readb(&priv->reg->control); + writeb(control | M48T35_RTC_SET, &priv->reg->control); + writeb(yrs, &priv->reg->year); + writeb(mon, &priv->reg->month); + writeb(day, &priv->reg->date); + writeb(hrs, &priv->reg->hour); + writeb(min, &priv->reg->min); + writeb(sec, &priv->reg->sec); + writeb(control, &priv->reg->control); + spin_unlock_irq(&priv->lock); + return 0; +} + +static const struct rtc_class_ops m48t35_ops = { + .read_time = m48t35_read_time, + .set_time = m48t35_set_time, +}; + +static int m48t35_probe(struct platform_device *pdev) +{ + struct resource *res; + struct m48t35_priv *priv; + + res = platform_get_resource(pdev, IORESOURCE_MEM, 0); + if (!res) + return -ENODEV; + priv = devm_kzalloc(&pdev->dev, sizeof(struct m48t35_priv), GFP_KERNEL); + if (!priv) + return -ENOMEM; + + priv->size = resource_size(res); + if (!devm_request_mem_region(&pdev->dev, res->start, priv->size, + pdev->name)) + return -EBUSY; + + priv->baseaddr = res->start; + priv->reg = devm_ioremap(&pdev->dev, priv->baseaddr, priv->size); + if (!priv->reg) + return -ENOMEM; + + spin_lock_init(&priv->lock); + + platform_set_drvdata(pdev, priv); + + priv->rtc = devm_rtc_device_register(&pdev->dev, "m48t35", + &m48t35_ops, THIS_MODULE); + return PTR_ERR_OR_ZERO(priv->rtc); +} + +static struct platform_driver m48t35_platform_driver = { + .driver = { + .name = "rtc-m48t35", + }, + .probe = m48t35_probe, +}; + +module_platform_driver(m48t35_platform_driver); + +MODULE_AUTHOR("Thomas Bogendoerfer "); +MODULE_DESCRIPTION("M48T35 RTC driver"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS("platform:rtc-m48t35"); -- cgit v1.3.1