On Thu, Feb 7, 2013 at 5:29 AM, Prarit Bhargava <pra...@redhat.com> wrote: > The problem with this model is what happens if /etc/adjtime is LOCAL, ie) > the rtc is set to localtime: > > Reboot the system, on the next boot, > rtc0_time = rtc + sys_tz.tz_minuteswest > Reboot the system, on the next boot, > rtc0_time = rtc + sys_tz.tz_minuteswest + sys_tz.tz_minuteswest > > AFAICT the only call to update_persistent_clock() in the kernel is the > ntp code. It is wired in to allow ntp to occasionally update the system > clock. Other calls to update the rtc are made directly through the > RTC_SET_TIME ioctl. > > I believe that the value passed into update_persistent_time() is wrong. It > should take into account the sys_tz data. If the rtc is UTC, then the > offset is 0. If the system is LOCAL, then there should be a 300 min offset > for the value of now. > > We do not see this manifest on some architectures because they limit changes > to the rtc to +/-15 minutes of the current value of the rtc (x86, alpha, > mn10300). Other arches do nothing (cris, mips, sh), and only a few seem to > show this problem (power, sparc). I can reproduce this reliably on powerpc > with the latest Fedoras (17, 18, rawhide), as well as an Ubuntu powerpc spin. > I can also reproduce it "older" OSes such as RHEL6.
Interesting. Yea, local RTC time is probably pretty rare outside of x86 (due to windows). And the +/- 15minute trick has always explicitly masked this issue there. > A few things about the patch. 'sys_time_offset' certainly could have a > better name and it could be a bool. Also, technically I do not need to add > the > 'adjust' struct in sync_cmos_clock() as the value of now.tv_sec is not used > after being passed into update_persistent_clock(). However, I think the code > is easier to follow if I do add 'adjust'. > > ------8<--------- > > Take the timezone offset applied in warp_clock() into account when writing > the hardware clock in the ntp code. This patch adds sys_time_offset which > indicates that an offset has been applied in warp_clock(). > > Signed-off-by: Prarit Bhargava <pra...@redhat.com> > Cc: John Stultz <johns...@us.ibm.com> > Cc: Thomas Gleixner <t...@linutronix.de> > --- > include/linux/time.h | 1 + > kernel/time.c | 8 ++++++++ > kernel/time/ntp.c | 8 ++++++-- > 3 files changed, 15 insertions(+), 2 deletions(-) > > diff --git a/include/linux/time.h b/include/linux/time.h > index 4d358e9..02754b5 100644 > --- a/include/linux/time.h > +++ b/include/linux/time.h > @@ -117,6 +117,7 @@ static inline bool timespec_valid_strict(const struct > timespec *ts) > > extern void read_persistent_clock(struct timespec *ts); > extern void read_boot_clock(struct timespec *ts); > +extern int sys_time_offset; > extern int update_persistent_clock(struct timespec now); > void timekeeping_init(void); > extern int timekeeping_suspended; > diff --git a/kernel/time.c b/kernel/time.c > index d226c6a..66533d3 100644 > --- a/kernel/time.c > +++ b/kernel/time.c > @@ -115,6 +115,12 @@ SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, > tv, > } > > /* > + * Indicates if there is an offset between the system clock and the hardware > + * clock/persistent clock/rtc. > + */ > +int sys_time_offset; So why is this extra flag necessary instead of just using if (sys_tz.tz_minuteswest) ? > + > +/* > * Adjust the time obtained from the CMOS to be UTC time instead of > * local time. > * > @@ -135,6 +141,8 @@ static inline void warp_clock(void) > struct timespec adjust; > > adjust = current_kernel_time(); > + if (sys_tz.tz_minuteswest > 0) > + sys_time_offset = 1; This seems like it wouldn't work for localtimes that are east of GMT. Or am I misunderstanding this? I feel like the warp_clock code has always been a bit unloved, and I've never worked out all the subtleties around it. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
