Messages in this thread Patch in this message | | | Subject | Re: [PATCH] timekeeping/vsyscall: Prevent math overflow in BOOTTIME update | From | Vincenzo Frascino <> | Date | Thu, 22 Aug 2019 17:05:00 +0100 |
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Hi Thomas,
On 22/08/2019 13:52, Chris Clayton wrote: > Thanks Thomas. > > On 22/08/2019 12:00, Thomas Gleixner wrote: >> The VDSO update for CLOCK_BOOTTIME has a overflow issue as it shifts the >> nanoseconds based boot time offset left by the clocksource shift. That >> overflows once the boot time offset becomes large enough. As a consequence >> CLOCK_BOOTTIME in the VDSO becomes a random number causing applications to >> misbehave. >> >> Fix it by storing a timespec64 representation of the offset when boot time >> is adjusted and add that to the MONOTONIC base time value in the vdso data >> page. Using the timespec64 representation avoids a 64bit division in the >> update code. >> > > I've tested resume from both suspend and hibernate and this patch fixes the problem I reported. > > Tested-by: Chris Clayton <chris2553@googlemail.com> >
I can confirm what reported by Chris. Please see below the scissors.
With this:
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
--->8---
Clock test start clk_id: CLOCK_BOOTTIME clock_getres: 0 1 clock_gettime:2697 489679147 2019-08-22 16:21:57.911 Clock test end
<...Suspend/Resume...>
Clock test start clk_id: CLOCK_BOOTTIME clock_getres: 0 1 clock_gettime:4489 684341925 2019-08-22 16:51:50.106 Clock test end
>> Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation") >> Reported-by: Chris Clayton <chris2553@googlemail.com> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> >> --- >> include/linux/timekeeper_internal.h | 5 +++++ >> kernel/time/timekeeping.c | 5 +++++ >> kernel/time/vsyscall.c | 22 +++++++++++++--------- >> 3 files changed, 23 insertions(+), 9 deletions(-) >> >> --- a/include/linux/timekeeper_internal.h >> +++ b/include/linux/timekeeper_internal.h >> @@ -57,6 +57,7 @@ struct tk_read_base { >> * @cs_was_changed_seq: The sequence number of clocksource change events >> * @next_leap_ktime: CLOCK_MONOTONIC time value of a pending leap-second >> * @raw_sec: CLOCK_MONOTONIC_RAW time in seconds >> + * @monotonic_to_boot: CLOCK_MONOTONIC to CLOCK_BOOTTIME offset >> * @cycle_interval: Number of clock cycles in one NTP interval >> * @xtime_interval: Number of clock shifted nano seconds in one NTP >> * interval. >> @@ -84,6 +85,9 @@ struct tk_read_base { >> * >> * wall_to_monotonic is no longer the boot time, getboottime must be >> * used instead. >> + * >> + * @monotonic_to_boottime is a timespec64 representation of @offs_boot to >> + * accelerate the VDSO update for CLOCK_BOOTTIME. >> */ >> struct timekeeper { >> struct tk_read_base tkr_mono; >> @@ -99,6 +103,7 @@ struct timekeeper { >> u8 cs_was_changed_seq; >> ktime_t next_leap_ktime; >> u64 raw_sec; >> + struct timespec64 monotonic_to_boot; >> >> /* The following members are for timekeeping internal use */ >> u64 cycle_interval; >> --- a/kernel/time/timekeeping.c >> +++ b/kernel/time/timekeeping.c >> @@ -146,6 +146,11 @@ static void tk_set_wall_to_mono(struct t >> static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta) >> { >> tk->offs_boot = ktime_add(tk->offs_boot, delta); >> + /* >> + * Timespec representation for VDSO update to avoid 64bit division >> + * on every update. >> + */ >> + tk->monotonic_to_boot = ktime_to_timespec64(tk->offs_boot); >> } >> >> /* >> --- a/kernel/time/vsyscall.c >> +++ b/kernel/time/vsyscall.c >> @@ -17,7 +17,7 @@ static inline void update_vdso_data(stru >> struct timekeeper *tk) >> { >> struct vdso_timestamp *vdso_ts; >> - u64 nsec; >> + u64 nsec, sec; >> >> vdata[CS_HRES_COARSE].cycle_last = tk->tkr_mono.cycle_last; >> vdata[CS_HRES_COARSE].mask = tk->tkr_mono.mask; >> @@ -45,23 +45,27 @@ static inline void update_vdso_data(stru >> } >> vdso_ts->nsec = nsec; >> >> - /* CLOCK_MONOTONIC_RAW */ >> - vdso_ts = &vdata[CS_RAW].basetime[CLOCK_MONOTONIC_RAW]; >> - vdso_ts->sec = tk->raw_sec; >> - vdso_ts->nsec = tk->tkr_raw.xtime_nsec; >> + /* Copy MONOTONIC time for BOOTTIME */ >> + sec = vdso_ts->sec; >> + /* Add the boot offset */ >> + sec += tk->monotonic_to_boot.tv_sec; >> + nsec += (u64)tk->monotonic_to_boot.tv_nsec << tk->tkr_mono.shift; >> >> /* CLOCK_BOOTTIME */ >> vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_BOOTTIME]; >> - vdso_ts->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec; >> - nsec = tk->tkr_mono.xtime_nsec; >> - nsec += ((u64)(tk->wall_to_monotonic.tv_nsec + >> - ktime_to_ns(tk->offs_boot)) << tk->tkr_mono.shift); >> + vdso_ts->sec = sec; >> + >> while (nsec >= (((u64)NSEC_PER_SEC) << tk->tkr_mono.shift)) { >> nsec -= (((u64)NSEC_PER_SEC) << tk->tkr_mono.shift); >> vdso_ts->sec++; >> } >> vdso_ts->nsec = nsec; >> >> + /* CLOCK_MONOTONIC_RAW */ >> + vdso_ts = &vdata[CS_RAW].basetime[CLOCK_MONOTONIC_RAW]; >> + vdso_ts->sec = tk->raw_sec; >> + vdso_ts->nsec = tk->tkr_raw.xtime_nsec; >> + >> /* CLOCK_TAI */ >> vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_TAI]; >> vdso_ts->sec = tk->xtime_sec + (s64)tk->tai_offset; >>
-- Regards, Vincenzo
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