From: Heena Sirwani Date: Wed, 29 Oct 2014 10:31:50 +0000 (+0530) Subject: timekeeping: Provide y2038 safe accessor to the seconds portion of CLOCK_REALTIME X-Git-Tag: firefly_0821_release~176^2~2752^2 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=dbe7aa622db96b5cd601f59d09c4f00b98b76079;p=firefly-linux-kernel-4.4.55.git timekeeping: Provide y2038 safe accessor to the seconds portion of CLOCK_REALTIME ktime_get_real_seconds() is the replacement function for get_seconds() returning the seconds portion of CLOCK_REALTIME in a time64_t. For 64bit the function is equivivalent to get_seconds(), but for 32bit it protects the readout with the timekeeper sequence count. This is required because 32-bit machines cannot access 64-bit tk->xtime_sec variable atomically. [tglx: Massaged changelog and added docbook comment ] Signed-off-by: Heena Sirwani Reviewed-by: Arnd Bergman Cc: John Stultz Cc: opw-kernel@googlegroups.com Link: http://lkml.kernel.org/r/7adcfaa8962b8ad58785d9a2456c3f77d93c0ffb.1414578445.git.heenasirwani@gmail.com Signed-off-by: Thomas Gleixner --- diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 115d55e11bc9..91454dea2bc6 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -29,6 +29,7 @@ struct timespec get_monotonic_coarse(void); extern void getrawmonotonic(struct timespec *ts); extern void ktime_get_ts64(struct timespec64 *ts); extern time64_t ktime_get_seconds(void); +extern time64_t ktime_get_real_seconds(void); extern int __getnstimeofday64(struct timespec64 *tv); extern void getnstimeofday64(struct timespec64 *tv); diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index a693270efafb..0aef92a0a701 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -676,6 +676,36 @@ time64_t ktime_get_seconds(void) } EXPORT_SYMBOL_GPL(ktime_get_seconds); +/** + * ktime_get_real_seconds - Get the seconds portion of CLOCK_REALTIME + * + * Returns the wall clock seconds since 1970. This replaces the + * get_seconds() interface which is not y2038 safe on 32bit systems. + * + * For 64bit systems the fast access to tk->xtime_sec is preserved. On + * 32bit systems the access must be protected with the sequence + * counter to provide "atomic" access to the 64bit tk->xtime_sec + * value. + */ +time64_t ktime_get_real_seconds(void) +{ + struct timekeeper *tk = &tk_core.timekeeper; + time64_t seconds; + unsigned int seq; + + if (IS_ENABLED(CONFIG_64BIT)) + return tk->xtime_sec; + + do { + seq = read_seqcount_begin(&tk_core.seq); + seconds = tk->xtime_sec; + + } while (read_seqcount_retry(&tk_core.seq, seq)); + + return seconds; +} +EXPORT_SYMBOL_GPL(ktime_get_real_seconds); + #ifdef CONFIG_NTP_PPS /**