Over the past years I've seen many reports of bugs that include time-stamped kernel logs (enabled when CONFIG_PRINTK_TIME=y or print.time=1 is specified as a kernel parameter) that do not align with either external time stamped logs or /var/log/messages. This also makes determining the time of a failure difficult in cases where /var/log/messages is unavailable.
For example, [root@intel-wildcatpass-06 ~]# date; echo "Hello!" > /dev/kmsg ; date Thu Jul 20 11:38:22 EST 2017 Thu Jul 20 11:38:22 EST 2017 which displays [83973.768912] Hello! on the serial console. Running a script to convert this to the stamped time, [root@intel-wildcatpass-06 ~]# ./human.sh | tail -1 [Thu July 17 11:39:45 2017] Hello! which is already off by 1 minute and 23 seconds off after ~24 hours of uptime. This occurs because the printk time stamp is obtained from a call to local_clock() which (on x86) is a direct call to the hardware. These hardware clock reads are not modified by the standard ntp or ptp protocol The other timestamps are and that results in situations external time sources are further and further offset from the kernel log timestamps. Implement printk.time settings to allow a user to specify the monotonic or real clocks. The default is the local clock (hardware clock). Real clock & 32-bit systems: Selecting the real clock printk timestamp may lead to unlikely situations where a timestamp is wrong because the real time offset is read without the protection of a sequence lock in the call to ktime_get_log_ts() in printk_get_ts(). Signed-off-by: Prarit Bhargava <[email protected]> Cc: Mark Salyzyn <[email protected]> Cc: Jonathan Corbet <[email protected]> Cc: Petr Mladek <[email protected]> Cc: Sergey Senozhatsky <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: John Stultz <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Stephen Boyd <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: Christoffer Dall <[email protected]> Cc: Deepa Dinamani <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Kees Cook <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Geert Uytterhoeven <[email protected]> Cc: "Luis R. Rodriguez" <[email protected]> Cc: Nicholas Piggin <[email protected]> Cc: "Jason A. Donenfeld" <[email protected]> Cc: Olof Johansson <[email protected]> Cc: "Theodore Ts'o" <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: [email protected] Prarit Bhargava (2): printk: Make CONFIG_PRINTK_TIME an int printk: Add boottime and real timestamps Documentation/admin-guide/kernel-parameters.txt | 6 +- arch/arm/configs/aspeed_g4_defconfig | 2 +- arch/arm/configs/aspeed_g5_defconfig | 2 +- arch/arm/configs/axm55xx_defconfig | 2 +- arch/arm/configs/bcm2835_defconfig | 2 +- arch/arm/configs/colibri_pxa270_defconfig | 2 +- arch/arm/configs/colibri_pxa300_defconfig | 2 +- arch/arm/configs/dove_defconfig | 2 +- arch/arm/configs/efm32_defconfig | 2 +- arch/arm/configs/exynos_defconfig | 2 +- arch/arm/configs/ezx_defconfig | 2 +- arch/arm/configs/h5000_defconfig | 2 +- arch/arm/configs/hisi_defconfig | 2 +- arch/arm/configs/imote2_defconfig | 2 +- arch/arm/configs/imx_v6_v7_defconfig | 2 +- arch/arm/configs/keystone_defconfig | 2 +- arch/arm/configs/lpc18xx_defconfig | 2 +- arch/arm/configs/magician_defconfig | 2 +- arch/arm/configs/mmp2_defconfig | 2 +- arch/arm/configs/moxart_defconfig | 2 +- arch/arm/configs/mps2_defconfig | 2 +- arch/arm/configs/multi_v7_defconfig | 2 +- arch/arm/configs/mvebu_v7_defconfig | 2 +- arch/arm/configs/mxs_defconfig | 2 +- arch/arm/configs/omap2plus_defconfig | 2 +- arch/arm/configs/pxa168_defconfig | 2 +- arch/arm/configs/pxa3xx_defconfig | 2 +- arch/arm/configs/pxa910_defconfig | 2 +- arch/arm/configs/pxa_defconfig | 2 +- arch/arm/configs/qcom_defconfig | 2 +- arch/arm/configs/raumfeld_defconfig | 2 +- arch/arm/configs/shmobile_defconfig | 2 +- arch/arm/configs/socfpga_defconfig | 2 +- arch/arm/configs/stm32_defconfig | 2 +- arch/arm/configs/sunxi_defconfig | 2 +- arch/arm/configs/tango4_defconfig | 2 +- arch/arm/configs/tegra_defconfig | 2 +- arch/arm/configs/u300_defconfig | 2 +- arch/arm/configs/u8500_defconfig | 2 +- arch/arm/configs/vt8500_v6_v7_defconfig | 2 +- arch/arm/configs/xcep_defconfig | 2 +- arch/arm/configs/zx_defconfig | 2 +- arch/arm64/configs/defconfig | 2 +- arch/m68k/configs/amcore_defconfig | 2 +- arch/mips/configs/ath25_defconfig | 2 +- arch/mips/configs/bcm47xx_defconfig | 2 +- arch/mips/configs/bmips_be_defconfig | 2 +- arch/mips/configs/bmips_stb_defconfig | 2 +- arch/mips/configs/ci20_defconfig | 2 +- arch/mips/configs/generic_defconfig | 2 +- arch/mips/configs/lemote2f_defconfig | 2 +- arch/mips/configs/loongson3_defconfig | 2 +- arch/mips/configs/nlm_xlp_defconfig | 2 +- arch/mips/configs/nlm_xlr_defconfig | 2 +- arch/mips/configs/pistachio_defconfig | 2 +- arch/mips/configs/qi_lb60_defconfig | 2 +- arch/mips/configs/rt305x_defconfig | 2 +- arch/mips/configs/xway_defconfig | 2 +- arch/parisc/configs/generic-64bit_defconfig | 2 +- arch/powerpc/configs/40x/virtex_defconfig | 2 +- arch/powerpc/configs/44x/fsp2_defconfig | 2 +- arch/powerpc/configs/44x/virtex5_defconfig | 2 +- arch/powerpc/configs/44x/warp_defconfig | 2 +- arch/powerpc/configs/52xx/cm5200_defconfig | 2 +- arch/powerpc/configs/52xx/lite5200b_defconfig | 2 +- arch/powerpc/configs/52xx/motionpro_defconfig | 2 +- arch/powerpc/configs/52xx/tqm5200_defconfig | 2 +- arch/powerpc/configs/gamecube_defconfig | 2 +- arch/powerpc/configs/mpc5200_defconfig | 2 +- arch/powerpc/configs/pasemi_defconfig | 2 +- arch/powerpc/configs/wii_defconfig | 2 +- arch/s390/configs/default_defconfig | 2 +- arch/s390/configs/gcov_defconfig | 2 +- arch/s390/configs/performance_defconfig | 2 +- arch/s390/configs/zfcpdump_defconfig | 2 +- arch/sh/configs/edosk7760_defconfig | 2 +- arch/sh/configs/sdk7786_defconfig | 2 +- arch/sh/configs/se7722_defconfig | 2 +- arch/sh/configs/sh7785lcr_32bit_defconfig | 2 +- arch/sh/configs/urquell_defconfig | 2 +- arch/sparc/configs/sparc64_defconfig | 2 +- arch/x86/configs/i386_defconfig | 2 +- arch/x86/configs/x86_64_defconfig | 2 +- arch/xtensa/configs/audio_kc705_defconfig | 2 +- arch/xtensa/configs/cadence_csp_defconfig | 2 +- arch/xtensa/configs/generic_kc705_defconfig | 2 +- arch/xtensa/configs/nommu_kc705_defconfig | 2 +- arch/xtensa/configs/smp_lx200_defconfig | 2 +- include/linux/timekeeping.h | 1 + kernel/printk/printk.c | 95 +++++++++++++++++++++- kernel/time/timekeeping.c | 14 ++++ lib/Kconfig.debug | 8 +- .../selftests/rcutorture/configs/lock/CFcommon | 2 +- .../selftests/rcutorture/configs/rcu/CFcommon | 2 +- .../selftests/rcutorture/configs/rcuperf/CFcommon | 2 +- 95 files changed, 206 insertions(+), 98 deletions(-) -- 1.8.5.5
