7bd3601446
Gerlando Falauto reported that when HRTICK is enabled, it is
possible to trigger system deadlocks. These were hard to
reproduce, as HRTICK has been broken in the past, but seemed
to be connected to the timekeeping_seq lock.
Since seqlock/seqcount's aren't supported w/ lockdep, I added
some extra spinlock based locking and triggered the following
lockdep output:
[ 15.849182] ntpd/4062 is trying to acquire lock:
[ 15.849765] (&(&pool->lock)->rlock){..-...}, at: [<ffffffff810aa9b5>] __queue_work+0x145/0x480
[ 15.850051]
[ 15.850051] but task is already holding lock:
[ 15.850051] (timekeeper_lock){-.-.-.}, at: [<ffffffff810df6df>] do_adjtimex+0x7f/0x100
<snip>
[ 15.850051] Chain exists of: &(&pool->lock)->rlock --> &p->pi_lock --> timekeeper_lock
[ 15.850051] Possible unsafe locking scenario:
[ 15.850051]
[ 15.850051] CPU0 CPU1
[ 15.850051] ---- ----
[ 15.850051] lock(timekeeper_lock);
[ 15.850051] lock(&p->pi_lock);
[ 15.850051] lock(timekeeper_lock);
[ 15.850051] lock(&(&pool->lock)->rlock);
[ 15.850051]
[ 15.850051] *** DEADLOCK ***
The deadlock was introduced by 06c017fdd4 ("timekeeping:
Hold timekeepering locks in do_adjtimex and hardpps") in 3.10
This patch avoids this deadlock, by moving the call to
schedule_delayed_work() outside of the timekeeper lock
critical section.
Reported-by: Gerlando Falauto <gerlando.falauto@keymile.com>
Tested-by: Lin Ming <minggr@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: stable <stable@vger.kernel.org> #3.11, 3.10
Link: http://lkml.kernel.org/r/1378943457-27314-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
149 lines
5.8 KiB
C
149 lines
5.8 KiB
C
/*****************************************************************************
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* *
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* Copyright (c) David L. Mills 1993 *
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* *
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* Permission to use, copy, modify, and distribute this software and its *
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* documentation for any purpose and without fee is hereby granted, provided *
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* that the above copyright notice appears in all copies and that both the *
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* copyright notice and this permission notice appear in supporting *
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* documentation, and that the name University of Delaware not be used in *
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* advertising or publicity pertaining to distribution of the software *
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* without specific, written prior permission. The University of Delaware *
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* makes no representations about the suitability this software for any *
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* purpose. It is provided "as is" without express or implied warranty. *
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* *
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*****************************************************************************/
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/*
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* Modification history timex.h
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*
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* 29 Dec 97 Russell King
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* Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h
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* for ARM machines
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*
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* 9 Jan 97 Adrian Sun
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* Shifted LATCH define to allow access to alpha machines.
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*
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* 26 Sep 94 David L. Mills
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* Added defines for hybrid phase/frequency-lock loop.
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*
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* 19 Mar 94 David L. Mills
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* Moved defines from kernel routines to header file and added new
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* defines for PPS phase-lock loop.
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*
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* 20 Feb 94 David L. Mills
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* Revised status codes and structures for external clock and PPS
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* signal discipline.
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*
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* 28 Nov 93 David L. Mills
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* Adjusted parameters to improve stability and increase poll
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* interval.
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*
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* 17 Sep 93 David L. Mills
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* Created file $NTP/include/sys/timex.h
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* 07 Oct 93 Torsten Duwe
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* Derived linux/timex.h
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* 1995-08-13 Torsten Duwe
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* kernel PLL updated to 1994-12-13 specs (rfc-1589)
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* 1997-08-30 Ulrich Windl
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* Added new constant NTP_PHASE_LIMIT
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* 2004-08-12 Christoph Lameter
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* Reworked time interpolation logic
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*/
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#ifndef _LINUX_TIMEX_H
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#define _LINUX_TIMEX_H
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#include <uapi/linux/timex.h>
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#define ADJ_ADJTIME 0x8000 /* switch between adjtime/adjtimex modes */
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#define ADJ_OFFSET_SINGLESHOT 0x0001 /* old-fashioned adjtime */
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#define ADJ_OFFSET_READONLY 0x2000 /* read-only adjtime */
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#include <linux/compiler.h>
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#include <linux/types.h>
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#include <linux/param.h>
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#include <asm/timex.h>
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/*
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* SHIFT_PLL is used as a dampening factor to define how much we
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* adjust the frequency correction for a given offset in PLL mode.
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* It also used in dampening the offset correction, to define how
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* much of the current value in time_offset we correct for each
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* second. Changing this value changes the stiffness of the ntp
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* adjustment code. A lower value makes it more flexible, reducing
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* NTP convergence time. A higher value makes it stiffer, increasing
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* convergence time, but making the clock more stable.
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*
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* In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
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* However this seems to increase convergence time much too long.
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*
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* https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
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*
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* In the above mailing list discussion, it seems the value of 4
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* was appropriate for other Unix systems with HZ=100, and that
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* SHIFT_PLL should be decreased as HZ increases. However, Linux's
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* clock steering implementation is HZ independent.
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*
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* Through experimentation, a SHIFT_PLL value of 2 was found to allow
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* for fast convergence (very similar to the NTPv3 code used prior to
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* v2.6.19), with good clock stability.
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*
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*
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* SHIFT_FLL is used as a dampening factor to define how much we
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* adjust the frequency correction for a given offset in FLL mode.
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* In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
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*
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* MAXTC establishes the maximum time constant of the PLL.
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*/
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#define SHIFT_PLL 2 /* PLL frequency factor (shift) */
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#define SHIFT_FLL 2 /* FLL frequency factor (shift) */
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#define MAXTC 10 /* maximum time constant (shift) */
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/*
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* SHIFT_USEC defines the scaling (shift) of the time_freq and
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* time_tolerance variables, which represent the current frequency
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* offset and maximum frequency tolerance.
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*/
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#define SHIFT_USEC 16 /* frequency offset scale (shift) */
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#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
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#define PPM_SCALE_INV_SHIFT 19
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#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
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PPM_SCALE + 1)
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#define MAXPHASE 500000000L /* max phase error (ns) */
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#define MAXFREQ 500000 /* max frequency error (ns/s) */
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#define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
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#define MINSEC 256 /* min interval between updates (s) */
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#define MAXSEC 2048 /* max interval between updates (s) */
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#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
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/*
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* kernel variables
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* Note: maximum error = NTP synch distance = dispersion + delay / 2;
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* estimated error = NTP dispersion.
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*/
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extern unsigned long tick_usec; /* USER_HZ period (usec) */
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extern unsigned long tick_nsec; /* SHIFTED_HZ period (nsec) */
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/* Required to safely shift negative values */
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#define shift_right(x, s) ({ \
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__typeof__(x) __x = (x); \
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__typeof__(s) __s = (s); \
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__x < 0 ? -(-__x >> __s) : __x >> __s; \
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})
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#define NTP_SCALE_SHIFT 32
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#define NTP_INTERVAL_FREQ (HZ)
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#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
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extern int do_adjtimex(struct timex *);
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extern void hardpps(const struct timespec *, const struct timespec *);
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int read_current_timer(unsigned long *timer_val);
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void ntp_notify_cmos_timer(void);
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/* The clock frequency of the i8253/i8254 PIT */
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#define PIT_TICK_RATE 1193182ul
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#endif /* LINUX_TIMEX_H */
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