Messages in this thread Patch in this message | | | From | Prarit Bhargava <> | Subject | [PATCH] printk, allow different timestamps for printk.time [v2] | Date | Thu, 28 Jan 2016 07:43:49 -0500 |
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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 Dec 17 13:58:31 EST 2015 Thu Dec 17 13:58:31 EST 2015
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 Dec 17 13:59:57 2015] Hello!
which is already off by 1 minute and 26 seconds off after ~24 hours of uptime.
This occurs because the 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, while the other timestamps are, and that results in situations external time sources are further and further offset from the kernel log timestamps.
This patch introduces printk.time=[0-3] allowing a user to specify an adjusted clock to use with printk timestamps. The hardware clock, or the existing functionality, is preserved by default.
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().
[v2]: use NMI safe timekeeping access functions [v3]: use tglx's ktime_get_log_ts() suggestion to get monotonic & real clocks [v4]: Fix kernel parameters
Cc: John Stultz <john.stultz@linaro.org> Cc: Xunlei Pang <pang.xunlei@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Baolin Wang <baolin.wang@linaro.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Petr Mladek <pmladek@suse.cz> Cc: Tejun Heo <tj@kernel.org> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Vasily Averin <vvs@virtuozzo.com> Cc: Joe Perches <joe@perches.com> Signed-off-by: Prarit Bhargava <prarit@redhat.com> --- Documentation/kernel-parameters.txt | 6 ++- include/linux/timekeeping.h | 1 + kernel/printk/printk.c | 79 +++++++++++++++++++++++++++++++++-- kernel/time/timekeeping.c | 13 ++++++ lib/Kconfig.debug | 2 +- 5 files changed, 94 insertions(+), 7 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 87d40a7..32f8dba 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3060,8 +3060,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. Format: <bool> (1/Y/y=enable, 0/N/n=disable) default: disabled - printk.time= Show timing data prefixed to each printk message line - Format: <bool> (1/Y/y=enable, 0/N/n=disable) + printk.time= Show timestamp prefixed to each printk message line + Format: <string> + (0/N/n = disable, 1/Y/y = local clock, + 2 = monotonic clock, 3 = real clock) processor.max_cstate= [HW,ACPI] Limit processor to maximum C-state diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index ec89d84..0b99a84 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -233,6 +233,7 @@ static inline u64 ktime_get_raw_ns(void) extern u64 ktime_get_mono_fast_ns(void); extern u64 ktime_get_raw_fast_ns(void); +extern u64 ktime_get_log_ts(u64 *offset_real); /* * Timespec interfaces utilizing the ktime based ones diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index c963ba5..19ec0d1 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -420,6 +420,8 @@ static u32 truncate_msg(u16 *text_len, u16 *trunc_msg_len, return msg_used_size(*text_len + *trunc_msg_len, 0, pad_len); } +static u64 printk_get_ts(void); + /* insert record into the buffer, discard old ones, update heads */ static int log_store(int facility, int level, enum log_flags flags, u64 ts_nsec, @@ -468,7 +470,7 @@ static int log_store(int facility, int level, if (ts_nsec > 0) msg->ts_nsec = ts_nsec; else - msg->ts_nsec = local_clock(); + msg->ts_nsec = printk_get_ts(); memset(log_dict(msg) + dict_len, 0, pad_len); msg->len = size; @@ -1035,8 +1037,77 @@ static inline void boot_delay_msec(int level) } #endif -static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME); -module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR); +static int printk_time = IS_ENABLED(CONFIG_PRINTK_TIME); + +/* + * 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() below. + */ +static int printk_time_param_set(const char *val, + const struct kernel_param *kp) +{ + char *param = strstrip((char *)val); + + if (strlen(param) != 1) + return -EINVAL; + + switch (param[0]) { + /* 0/N/n = disabled */ + case '0': + case 'N': + case 'n': + printk_time = 0; + break; + /* 1/Y/y = local clock */ + case '1': + case 'Y': + case 'y': + printk_time = 1; + break; + /* 2 = monotonic clock */ + case '2': + printk_time = 2; + break; + /* 3 = real clock */ + case '3': + printk_time = 3; + break; + default: + pr_warn("printk: invalid timestamp value\n"); + return -EINVAL; + break; + } + + pr_info("printk: timestamp set to %d.\n", printk_time); + return 0; +} + +static struct kernel_param_ops printk_time_param_ops = { + .set = printk_time_param_set, + .get = param_get_int, +}; + +module_param_cb(time, &printk_time_param_ops, &printk_time, S_IRUGO | S_IWUSR); + +static u64 printk_get_ts(void) +{ + u64 mono, offset_real; + + if (printk_time == 0) + return 0; + + if (printk_time == 1) + return local_clock(); + + mono = ktime_get_log_ts(&offset_real); + + if (printk_time == 2) + return mono; + + return mono + offset_real; +} static size_t print_time(u64 ts, char *buf) { @@ -1614,7 +1685,7 @@ static bool cont_add(int facility, int level, const char *text, size_t len) cont.facility = facility; cont.level = level; cont.owner = current; - cont.ts_nsec = local_clock(); + cont.ts_nsec = printk_get_ts(); cont.flags = 0; cont.cons = 0; cont.flushed = false; diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 34b4ced..698e1a2 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -43,6 +43,7 @@ static struct { static DEFINE_RAW_SPINLOCK(timekeeper_lock); static struct timekeeper shadow_timekeeper; +static int timekeeping_active; /** * struct tk_fast - NMI safe timekeeper @@ -401,6 +402,16 @@ u64 ktime_get_raw_fast_ns(void) } EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns); +u64 ktime_get_log_ts(u64 *offset_real) +{ + *offset_real = ktime_to_ns(tk_core.timekeeper.offs_real); + + if (timekeeping_active) + return ktime_get_mono_fast_ns(); + else + return local_clock(); +} + /* Suspend-time cycles value for halted fast timekeeper. */ static cycle_t cycles_at_suspend; @@ -1267,6 +1278,8 @@ void __init timekeeping_init(void) write_seqcount_end(&tk_core.seq); raw_spin_unlock_irqrestore(&timekeeper_lock, flags); + + timekeeping_active = 1; } /* time in seconds when suspend began for persistent clock */ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index ecb9e75..6d0ddb0 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -13,7 +13,7 @@ config PRINTK_TIME be included, not that the timestamp is recorded. The behavior is also controlled by the kernel command line - parameter printk.time=1. See Documentation/kernel-parameters.txt + parameter printk.time=[0-3]. See Documentation/kernel-parameters.txt config MESSAGE_LOGLEVEL_DEFAULT int "Default message log level (1-7)" -- 1.7.9.3
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