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-max6902.c | 154 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 154 insertions(+) create mode 100644 drivers/rtc/rtc-max6902.c (limited to 'drivers/rtc/rtc-max6902.c') diff --git a/drivers/rtc/rtc-max6902.c b/drivers/rtc/rtc-max6902.c new file mode 100644 index 000000000..daaeb6fb6 --- /dev/null +++ b/drivers/rtc/rtc-max6902.c @@ -0,0 +1,154 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* drivers/rtc/rtc-max6902.c + * + * Copyright (C) 2006 8D Technologies inc. + * Copyright (C) 2004 Compulab Ltd. + * + * Driver for MAX6902 spi RTC + */ + +#include +#include +#include +#include +#include +#include +#include + +#define MAX6902_REG_SECONDS 0x01 +#define MAX6902_REG_MINUTES 0x03 +#define MAX6902_REG_HOURS 0x05 +#define MAX6902_REG_DATE 0x07 +#define MAX6902_REG_MONTH 0x09 +#define MAX6902_REG_DAY 0x0B +#define MAX6902_REG_YEAR 0x0D +#define MAX6902_REG_CONTROL 0x0F +#define MAX6902_REG_CENTURY 0x13 + +static int max6902_set_reg(struct device *dev, unsigned char address, + unsigned char data) +{ + struct spi_device *spi = to_spi_device(dev); + unsigned char buf[2]; + + /* MSB must be '0' to write */ + buf[0] = address & 0x7f; + buf[1] = data; + + return spi_write_then_read(spi, buf, 2, NULL, 0); +} + +static int max6902_get_reg(struct device *dev, unsigned char address, + unsigned char *data) +{ + struct spi_device *spi = to_spi_device(dev); + + /* Set MSB to indicate read */ + *data = address | 0x80; + + return spi_write_then_read(spi, data, 1, data, 1); +} + +static int max6902_read_time(struct device *dev, struct rtc_time *dt) +{ + int err, century; + struct spi_device *spi = to_spi_device(dev); + unsigned char buf[8]; + + buf[0] = 0xbf; /* Burst read */ + + err = spi_write_then_read(spi, buf, 1, buf, 8); + if (err != 0) + return err; + + /* The chip sends data in this order: + * Seconds, Minutes, Hours, Date, Month, Day, Year */ + dt->tm_sec = bcd2bin(buf[0]); + dt->tm_min = bcd2bin(buf[1]); + dt->tm_hour = bcd2bin(buf[2]); + dt->tm_mday = bcd2bin(buf[3]); + dt->tm_mon = bcd2bin(buf[4]) - 1; + dt->tm_wday = bcd2bin(buf[5]); + dt->tm_year = bcd2bin(buf[6]); + + /* Read century */ + err = max6902_get_reg(dev, MAX6902_REG_CENTURY, &buf[0]); + if (err != 0) + return err; + + century = bcd2bin(buf[0]) * 100; + + dt->tm_year += century; + dt->tm_year -= 1900; + + return 0; +} + +static int max6902_set_time(struct device *dev, struct rtc_time *dt) +{ + dt->tm_year = dt->tm_year + 1900; + + /* Remove write protection */ + max6902_set_reg(dev, MAX6902_REG_CONTROL, 0); + + max6902_set_reg(dev, MAX6902_REG_SECONDS, bin2bcd(dt->tm_sec)); + max6902_set_reg(dev, MAX6902_REG_MINUTES, bin2bcd(dt->tm_min)); + max6902_set_reg(dev, MAX6902_REG_HOURS, bin2bcd(dt->tm_hour)); + + max6902_set_reg(dev, MAX6902_REG_DATE, bin2bcd(dt->tm_mday)); + max6902_set_reg(dev, MAX6902_REG_MONTH, bin2bcd(dt->tm_mon + 1)); + max6902_set_reg(dev, MAX6902_REG_DAY, bin2bcd(dt->tm_wday)); + max6902_set_reg(dev, MAX6902_REG_YEAR, bin2bcd(dt->tm_year % 100)); + max6902_set_reg(dev, MAX6902_REG_CENTURY, bin2bcd(dt->tm_year / 100)); + + /* Compulab used a delay here. However, the datasheet + * does not mention a delay being required anywhere... */ + /* delay(2000); */ + + /* Write protect */ + max6902_set_reg(dev, MAX6902_REG_CONTROL, 0x80); + + return 0; +} + +static const struct rtc_class_ops max6902_rtc_ops = { + .read_time = max6902_read_time, + .set_time = max6902_set_time, +}; + +static int max6902_probe(struct spi_device *spi) +{ + struct rtc_device *rtc; + unsigned char tmp; + int res; + + spi->mode = SPI_MODE_3; + spi->bits_per_word = 8; + spi_setup(spi); + + res = max6902_get_reg(&spi->dev, MAX6902_REG_SECONDS, &tmp); + if (res != 0) + return res; + + rtc = devm_rtc_device_register(&spi->dev, "max6902", + &max6902_rtc_ops, THIS_MODULE); + if (IS_ERR(rtc)) + return PTR_ERR(rtc); + + spi_set_drvdata(spi, rtc); + return 0; +} + +static struct spi_driver max6902_driver = { + .driver = { + .name = "rtc-max6902", + }, + .probe = max6902_probe, +}; + +module_spi_driver(max6902_driver); + +MODULE_DESCRIPTION("max6902 spi RTC driver"); +MODULE_AUTHOR("Raphael Assenat"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS("spi:rtc-max6902"); -- cgit v1.3.1