kernel.git/include/linux/timex.h, branch linux-2.6.32.y

ntp: Fix leap-second hrtimer livelock

2012-10-07T21:37:04Z

This is a backport of 6b43ae8a619d17c4935c3320d2ef9e92bdeed05d This should have been backported when it was commited, but I mistook the problem as requiring the ntp_lock changes that landed in 3.4 in order for it to occur. Unfortunately the same issue can happen (with only one cpu) as follows: do_adjtimex() write_seqlock_irq(&xtime_lock); process_adjtimex_modes() process_adj_status() ntp_start_leap_timer() hrtimer_start() hrtimer_reprogram() tick_program_event() clockevents_program_event() ktime_get() seq = req_seqbegin(xtime_lock); [DEADLOCK] This deadlock will no always occur, as it requires the leap_timer to force a hrtimer_reprogram which only happens if its set and there's no sooner timer to expire. NOTE: This patch, being faithful to the original commit, introduces a bug (we don't update wall_to_monotonic), which will be resovled by backporting a following fix. Original commit message below: Since commit 7dffa3c673fbcf835cd7be80bb4aec8ad3f51168 the ntp subsystem has used an hrtimer for triggering the leapsecond adjustment. However, this can cause a potential livelock. Thomas diagnosed this as the following pattern: CPU 0 CPU 1 do_adjtimex() spin_lock_irq(&ntp_lock); process_adjtimex_modes(); timer_interrupt() process_adj_status(); do_timer() ntp_start_leap_timer(); write_lock(&xtime_lock); hrtimer_start(); update_wall_time(); hrtimer_reprogram(); ntp_tick_length() tick_program_event() spin_lock(&ntp_lock); clockevents_program_event() ktime_get() seq = req_seqbegin(xtime_lock); This patch tries to avoid the problem by reverting back to not using an hrtimer to inject leapseconds, and instead we handle the leapsecond processing in the second_overflow() function. The downside to this change is that on systems that support highres timers, the leap second processing will occur on a HZ tick boundary, (ie: ~1-10ms, depending on HZ) after the leap second instead of possibly sooner (~34us in my tests w/ x86_64 lapic). This patch applies on top of tip/timers/core. CC: Sasha Levin CC: Thomas Gleixner Reported-by: Sasha Levin Diagnoised-by: Thomas Gleixner Tested-by: Sasha Levin Cc: Prarit Bhargava Cc: Thomas Gleixner Cc: Linux Kernel Signed-off-by: John Stultz Signed-off-by: Willy Tarreau

time: move PIT_TICK_RATE to linux/timex.h

2009-06-17T02:47:27Z

PIT_TICK_RATE is currently defined in four architectures, but in three different places. While linux/timex.h is not the perfect place for it, it is still a reasonable replacement for those drivers that traditionally use asm/timex.h to get CLOCK_TICK_RATE and expect it to be the PIT frequency. Note that for Alpha, the actual value changed from 1193182UL to 1193180UL. This is unlikely to make a difference, and probably can only improve accuracy. There was a discussion on the correct value of CLOCK_TICK_RATE a few years ago, after which every existing instance was getting changed to 1193182. According to the specification, it should be 1193181.818181... Signed-off-by: Arnd Bergmann Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Ralf Baechle Cc: Benjamin Herrenschmidt Cc: Ingo Molnar Cc: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Len Brown Cc: john stultz Cc: Dmitry Torokhov Cc: Takashi Iwai Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ntp: fix comment typos

2009-05-12T08:35:15Z

Bernhard Schiffner noticed I had a few comment typos in this patch, (note: to save embarrassment, when making typos, avoid copying and pasting them) so this patch corrects them. [ Impact: cleanup ] Reported-by: Bernhard Schiffner Signed-off-by: John Stultz Cc: riel@redhat.com Cc: akpm@linux-foundation.org LKML-Reference: <1242090794.7214.131.camel@localhost.localdomain> Signed-off-by: Ingo Molnar

ntp: adjust SHIFT_PLL to improve NTP convergence

2009-05-06T09:44:02Z

The conversion to the ntpv4 reference model f19923937321244e7dc334767eb4b67e0e3d5c74 ("ntp: convert to the NTP4 reference model") in 2.6.19 added nanosecond resolution the adjtimex interface, but also changed the "stiffness" of the frequency adjustments, causing NTP convergence time to greatly increase. SHIFT_PLL, which reduces the stiffness of the freq adjustments, was designed to be inversely linked to HZ, and the reference value of 4 was designed for Unix systems using HZ=100. However Linux's clock steering code mostly independent of HZ. So this patch reduces the SHIFT_PLL value from 4 to 2, which causes NTPd behavior to match kernels prior to 2.6.19, greatly reducing convergence times, and improving close synchronization through environmental thermal changes. The patch also changes some l's to L's in nearby code to avoid misreading 50l as 501. [ Impact: tweak NTP algorithm for faster convergence ] Signed-off-by: John Stultz Acked-by: Rik van Riel Cc: zippel@linux-m68k.org Signed-off-by: Andrew Morton LKML-Reference: <200905051956.n45JuVo9025575@imap1.linux-foundation.org> Signed-off-by: Ingo Molnar

time: ntp: make 64-bit constants more robust

2009-02-25T17:38:15Z

Impact: cleanup, no functionality changed - make PPM_SCALE an explicit s64 constant, to remove (s64) casts from usage sites. kernel/time/ntp.o: text data bss dec hex filename 2536 114 136 2786 ae2 ntp.o.before 2536 114 136 2786 ae2 ntp.o.after md5: 40a7728d1188aa18e83e21a81fa7b150 ntp.o.before.asm 40a7728d1188aa18e83e21a81fa7b150 ntp.o.after.asm Signed-off-by: Ingo Molnar

linux/timex.h: cleanup for userspace

2008-12-12T16:01:38Z

Impact: fix user-space exported use Move all the kernel-specific defines and includes into the __KERNEL__ section so that they don't get leaked into userspace. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Mike Frysinger Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner

ntp: improve adjtimex frequency rounding

2008-09-24T15:33:13Z

Change PPM_SCALE_INV_SHIFT so that it doesn't throw away any input bits (19 is the amount of the factor 2 in PPM_SCALE), the output frequency can then be calculated back to its input value, as the inverse divide produce a slightly larger value, which is then correctly rounded by the final shift. Reported-by: Martin Ziegler Signed-off-by: Roman Zippel Cc: John Stultz Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner

ntp: fix ADJ_OFFSET_SS_READ bug and do_adjtimex() cleanup

2008-08-22T04:40:18Z

Thanks to the review by Michael Kerrisk a bug in the recent ADJ_OFFSET_SS_READ option was discovered, where the ntp time_offset was inadvertently set by it. This fixes this by making the adjtime code more separate from the ntp_adjtime code (both of which really want to be separate syscalls). Signed-off-by: Roman Zippel Signed-off-by: Andrew Morton Acked-by: John Stultz Signed-off-by: Ingo Molnar

ntp: handle leap second via timer

2008-05-01T15:03:59Z

Remove the leap second handling from second_overflow(), which doesn't have to check for it every second anymore. With CONFIG_NO_HZ this also makes sure the leap second is handled close to the full second. Additionally this makes it possible to abort a leap second properly by resetting the STA_INS/STA_DEL status bits. Signed-off-by: Roman Zippel Cc: john stultz Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ntp: remove current_tick_length()

2008-05-01T15:03:59Z

current_tick_length used to do a little more, but now it just returns tick_length, which we can also access directly at the few places, where it's needed. Signed-off-by: Roman Zippel Cc: john stultz Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds