Re: [PATCH] um: time-travel: fix time going backwards

[Vincent Whitchurch]

On Mon, 2023-10-23 at 09:33 +0200, Johannes Berg wrote:
> Do you have a specific workload that tends to reproduce this?

I've been seeing it when running roadtest, but it's easily reproducible
without that by using the attached config and the following program as
init.

  cp repro.config .config
  make ARCH=um olddefconfig all
  gcc -Wall -static -o repro repro.c
  ./linux time-travel init=$PWD/repro rootfstype=hostfs

With the above commands I usually see the panic in a few seconds.  This
is on an unmodified v6.6-rc7.

----8<-------
#include <time.h>
#include <pthread.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>

int main(void)
{
        if (fork() == 0) {
                while (1) {
                        nanosleep(&(struct timespec){.tv_nsec = 330 * 1000}, NULL);
                }
                return 0;
        }
        
        while (1) {
                struct timespec ts;
                clock_gettime(CLOCK_MONOTONIC, &ts);
                nanosleep(&(struct timespec){.tv_nsec = 22 * 1000}, NULL);
        }
        
        return 0;
}       
# CONFIG_LOCALVERSION_AUTO is not set
CONFIG_NO_HZ=y
CONFIG_HIGH_RES_TIMERS=y
CONFIG_LOG_BUF_SHIFT=18
CONFIG_EXPERT=y
CONFIG_HOSTFS=y
CONFIG_MAGIC_SYSRQ=y
CONFIG_UML_TIME_TRAVEL_SUPPORT=y
CONFIG_SSL=y
CONFIG_NULL_CHAN=y
CONFIG_PORT_CHAN=y
CONFIG_PTY_CHAN=y
CONFIG_TTY_CHAN=y
CONFIG_XTERM_CHAN=y
CONFIG_CON_CHAN="pts"
CONFIG_SSL_CHAN="pts"
CONFIG_VIRTIO_UML=y
CONFIG_UML_PCI_OVER_VIRTIO=y
CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID=1234
CONFIG_GCOV_KERNEL=y
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
CONFIG_BINFMT_MISC=m
# CONFIG_COMPACTION is not set
CONFIG_NET=y
CONFIG_UNIX=y
CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y
CONFIG_OF=y
# CONFIG_INPUT is not set
CONFIG_LEGACY_PTY_COUNT=32
CONFIG_SERIAL_SC16IS7XX=m
CONFIG_GOLDFISH_TTY=m
CONFIG_SERIAL_DEV_BUS=y
CONFIG_UML_RANDOM=y
# CONFIG_I2C_COMPAT is not set
CONFIG_I2C_CHARDEV=y
CONFIG_I2C_VIRTIO=y
CONFIG_I2C_STUB=m
CONFIG_SPI=y
CONFIG_SPI_SC18IS602=y
CONFIG_SPI_MUX=y
CONFIG_PINCTRL=y
CONFIG_GPIOLIB=y
CONFIG_GPIO_SYSFS=y
CONFIG_GPIO_GENERIC_PLATFORM=m
CONFIG_GPIO_MOCKUP=y
CONFIG_GPIO_VIRTIO=y
CONFIG_POWER_SUPPLY=y
CONFIG_CHARGER_BQ256XX=m
CONFIG_PMBUS=y
CONFIG_SENSORS_LTC2978=m
CONFIG_SENSORS_LTC2978_REGULATOR=y
CONFIG_SENSORS_PWM_FAN=m
CONFIG_SENSORS_TMP401=m
CONFIG_REGULATOR=y
CONFIG_REGULATOR_DEBUG=y
CONFIG_REGULATOR_FIXED_VOLTAGE=y
CONFIG_REGULATOR_VIRTUAL_CONSUMER=m
CONFIG_REGULATOR_GPIO=m
CONFIG_REGULATOR_TPS6286X=m
CONFIG_REGULATOR_TPS6287X=m
CONFIG_DRM=y
CONFIG_TINYDRM_ILI9341=m
CONFIG_NEW_LEDS=y
CONFIG_LEDS_CLASS=y
CONFIG_LEDS_GPIO=y
CONFIG_LEDS_TRIGGERS=y
CONFIG_LEDS_TRIGGER_HEARTBEAT=y
CONFIG_RTC_CLASS=y
# CONFIG_RTC_HCTOSYS is not set
# CONFIG_RTC_SYSTOHC is not set
CONFIG_RTC_DEBUG=y
CONFIG_RTC_DRV_PCF8523=m
CONFIG_RTC_DRV_PCF8563=m
CONFIG_GOLDFISH=y
CONFIG_COMMON_CLK=y
CONFIG_COMMON_CLK_SI5351=m
CONFIG_IIO=y
CONFIG_IIO_BUFFER_CB=m
CONFIG_IIO_SW_TRIGGER=y
CONFIG_MCP320X=m
CONFIG_TI_ADC081C=m
CONFIG_TI_ADC084S021=m
CONFIG_TI_ADS7924=m
CONFIG_PMS7003=m
CONFIG_OPT3001=m
CONFIG_OPT4001=m
CONFIG_VCNL4000=m
CONFIG_IIO_HRTIMER_TRIGGER=y
CONFIG_IIO_SYSFS_TRIGGER=y
CONFIG_IRSD200=m
CONFIG_PWM=y
CONFIG_PWM_PCA9685=m
CONFIG_MUX_GPIO=y
CONFIG_QUOTA=y
CONFIG_PROC_KCORE=y
CONFIG_TMPFS=y
CONFIG_NLS=y
CONFIG_CRYPTO=y
CONFIG_CRYPTO_CRC32C=y
CONFIG_CRYPTO_JITTERENTROPY=y
CONFIG_CRC16=y
CONFIG_PRINTK_TIME=y
CONFIG_PRINTK_CALLER=y
CONFIG_DYNAMIC_DEBUG=y
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
CONFIG_GDB_SCRIPTS=y
CONFIG_FRAME_WARN=1024
CONFIG_READABLE_ASM=y
CONFIG_DEBUG_FS=y
CONFIG_UBSAN=y
CONFIG_PAGE_EXTENSION=y
CONFIG_DEBUG_OBJECTS=y
CONFIG_DEBUG_OBJECTS_FREE=y
CONFIG_DEBUG_OBJECTS_TIMERS=y
CONFIG_DEBUG_OBJECTS_WORK=y
CONFIG_KASAN=y
CONFIG_PROVE_LOCKING=y
CONFIG_ENABLE_DEFAULT_TRACERS=y
CONFIG_FAULT_INJECTION=y
CONFIG_FAILSLAB=y
CONFIG_FAULT_INJECTION_DEBUG_FS=y
CONFIG_FAULT_INJECTION_STACKTRACE_FILTER=y