linux-stable.git/kernel/time/timekeeping.c, branch v4.14.331

timekeeping: Add raw clock fallback for random_get_entropy()

2022-06-25T09:46:38+00:00

commit 1366992e16bddd5e2d9a561687f367f9f802e2e4 upstream.

The addition of random_get_entropy_fallback() provides access to
whichever time source has the highest frequency, which is useful for
gathering entropy on platforms without available cycle counters. It's
not necessarily as good as being able to quickly access a cycle counter
that the CPU has, but it's still something, even when it falls back to
being jiffies-based.

In the event that a given arch does not define get_cycles(), falling
back to the get_cycles() default implementation that returns 0 is really
not the best we can do. Instead, at least calling
random_get_entropy_fallback() would be preferable, because that always
needs to return _something_, even falling back to jiffies eventually.
It's not as though random_get_entropy_fallback() is super high precision
or guaranteed to be entropic, but basically anything that's not zero all
the time is better than returning zero all the time.

Finally, since random_get_entropy_fallback() is used during extremely
early boot when randomizing freelists in mm_init(), it can be called
before timekeeping has been initialized. In that case there really is
nothing we can do; jiffies hasn't even started ticking yet. So just give
up and return 0.

Suggested-by: Thomas Gleixner 
Signed-off-by: Jason A. Donenfeld 
Reviewed-by: Thomas Gleixner 
Cc: Arnd Bergmann 
Cc: Theodore Ts'o 
Signed-off-by: Jason A. Donenfeld 
Signed-off-by: Greg Kroah-Hartman

timekeeping: Really make sure wall_to_monotonic isn't positive

2021-12-22T08:18:00+00:00

commit 4e8c11b6b3f0b6a283e898344f154641eda94266 upstream.

Even after commit e1d7ba873555 ("time: Always make sure wall_to_monotonic
isn't positive") it is still possible to make wall_to_monotonic positive
by running the following code:

    int main(void)
    {
        struct timespec time;

        clock_gettime(CLOCK_MONOTONIC, &time);
        time.tv_nsec = 0;
        clock_settime(CLOCK_REALTIME, &time);
        return 0;
    }

The reason is that the second parameter of timespec64_compare(), ts_delta,
may be unnormalized because the delta is calculated with an open coded
substraction which causes the comparison of tv_sec to yield the wrong
result:

  wall_to_monotonic = { .tv_sec = -10, .tv_nsec =  900000000 }
  ts_delta 	    = { .tv_sec =  -9, .tv_nsec = -900000000 }

That makes timespec64_compare() claim that wall_to_monotonic < ts_delta,
but actually the result should be wall_to_monotonic > ts_delta.

After normalization, the result of timespec64_compare() is correct because
the tv_sec comparison is not longer misleading:

  wall_to_monotonic = { .tv_sec = -10, .tv_nsec =  900000000 }
  ts_delta 	    = { .tv_sec = -10, .tv_nsec =  100000000 }

Use timespec64_sub() to ensure that ts_delta is normalized, which fixes the
issue.

Fixes: e1d7ba873555 ("time: Always make sure wall_to_monotonic isn't positive")
Signed-off-by: Yu Liao 
Signed-off-by: Thomas Gleixner 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211213135727.1656662-1-liaoyu15@huawei.com
Signed-off-by: Greg Kroah-Hartman

timekeeping: Prevent 32bit truncation in scale64_check_overflow()

2020-10-01T11:12:36+00:00

[ Upstream commit 4cbbc3a0eeed675449b1a4d080008927121f3da3 ]

While unlikely the divisor in scale64_check_overflow() could be >= 32bit in
scale64_check_overflow(). do_div() truncates the divisor to 32bit at least
on 32bit platforms.

Use div64_u64() instead to avoid the truncation to 32-bit.

[ tglx: Massaged changelog ]

Signed-off-by: Wen Yang 
Signed-off-by: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20200120100523.45656-1-wenyang@linux.alibaba.com
Signed-off-by: Sasha Levin

timekeeping: Use proper seqcount initializer

2019-02-12T18:46:01+00:00

[ Upstream commit ce10a5b3954f2514af726beb78ed8d7350c5e41c ]

tk_core.seq is initialized open coded, but that misses to initialize the
lockdep map when lockdep is enabled. Lockdep splats involving tk_core seq
consequently lack a name and are hard to read.

Use the proper initializer which takes care of the lockdep map
initialization.

[ tglx: Massaged changelog ]

Signed-off-by: Bart Van Assche 
Signed-off-by: Thomas Gleixner 
Cc: peterz@infradead.org
Cc: tj@kernel.org
Cc: johannes.berg@intel.com
Link: https://lkml.kernel.org/r/20181128234325.110011-12-bvanassche@acm.org
Signed-off-by: Sasha Levin

drivers/pps: aesthetic tweaks to PPS-related content

2017-09-09T01:26:51+00:00

Collection of aesthetic adjustments to various PPS-related files,
directories and Documentation, some quite minor just for the sake of
consistency, including:

 * Updated example of pps device tree node (courtesy Rodolfo G.)
 * "PPS-API" -> "PPS API"
 * "pps_source_info_s" -> "pps_source_info"
 * "ktimer driver" -> "pps-ktimer driver"
 * "ppstest /dev/pps0" -> "ppstest /dev/pps1" to match example
 * Add missing PPS-related entries to MAINTAINERS file
 * Other trivialities

Link: http://lkml.kernel.org/r/alpine.LFD.2.20.1708261048220.8106@localhost.localdomain
Signed-off-by: Robert P. J. Day 
Acked-by: Rodolfo Giometti 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2017-09-04T20:06:34+00:00

Pull timer fixes from Thomas Gleixner:
 "A rather small update for the time(r) subsystem:

   - A new clocksource driver IMX-TPM

   - Minor fixes to the alarmtimer facility

   - Device tree cleanups for Renesas drivers

   - A new kselftest and fixes for the timer related tests

   - Conversion of the clocksource drivers to use %pOF

   - Use the proper helpers to access rlimits in the posix-cpu-timer
     code"

* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  alarmtimer: Ensure RTC module is not unloaded
  clocksource: Convert to using %pOF instead of full_name
  clocksource/drivers/bcm2835: Remove message for a memory allocation failure
  devicetree: bindings: Remove deprecated properties
  devicetree: bindings: Remove unused 32-bit CMT bindings
  devicetree: bindings: Deprecate property, update example
  devicetree: bindings: r8a73a4 and R-Car Gen2 CMT bindings
  devicetree: bindings: R-Car Gen2 CMT0 and CMT1 bindings
  devicetree: bindings: Remove sh7372 CMT binding
  clocksource/drivers/imx-tpm: Add imx tpm timer support
  dt-bindings: timer: Add nxp tpm timer binding doc
  posix-cpu-timers: Use dedicated helper to access rlimit values
  alarmtimer: Fix unavailable wake-up source in sysfs
  timekeeping: Use proper timekeeper for debug code
  kselftests: timers: set-timer-lat: Add one-shot timer test cases
  kselftests: timers: set-timer-lat: Tweak reporting when timer fires early
  kselftests: timers: freq-step: Fix build warning
  kselftests: timers: freq-step: Define ADJ_SETOFFSET if device has older kernel headers

time: Fix ktime_get_raw() incorrect base accumulation

2017-08-26T14:06:12+00:00

In comqit fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time
handling"), the following code got mistakenly added to the update of the
raw timekeeper:

 /* Update the monotonic raw base */
 seconds = tk->raw_sec;
 nsec = (u32)(tk->tkr_raw.xtime_nsec >> tk->tkr_raw.shift);
 tk->tkr_raw.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);

Which adds the raw_sec value and the shifted down raw xtime_nsec to the
base value.

But the read function adds the shifted down tk->tkr_raw.xtime_nsec value
another time, The result of this is that ktime_get_raw() users (which are
all internal users) see the raw time move faster then it should (the rate
at which can vary with the current size of tkr_raw.xtime_nsec), which has
resulted in at least problems with graphics rendering performance.

The change tried to match the monotonic base update logic:

 seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec);
 nsec = (u32) tk->wall_to_monotonic.tv_nsec;
 tk->tkr_mono.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);

Which adds the wall_to_monotonic.tv_nsec value, but not the
tk->tkr_mono.xtime_nsec value to the base.

To fix this, simplify the tkr_raw.base accumulation to only accumulate the
raw_sec portion, and do not include the tkr_raw.xtime_nsec portion, which
will be added at read time.

Fixes: fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time handling")
Reported-and-tested-by: Chris Wilson 
Signed-off-by: John Stultz 
Signed-off-by: Thomas Gleixner 
Cc: Prarit Bhargava 
Cc: Kevin Brodsky 
Cc: Richard Cochran 
Cc: Stephen Boyd 
Cc: Will Deacon 
Cc: Miroslav Lichvar 
Cc: Daniel Mentz 
Link: http://lkml.kernel.org/r/1503701824-1645-1-git-send-email-john.stultz@linaro.org

timekeeping: Use proper timekeeper for debug code

2017-08-17T19:15:04+00:00

When CONFIG_DEBUG_TIMEKEEPING is enabled the timekeeping_check_update()
function will update status like last_warning and underflow_seen on the
timekeeper.

If there are issues found this state is used to rate limit the warnings
that get printed.

This rate limiting doesn't really really work if stored in real_tk as
the shadow timekeeper is overwritten onto real_tk at the end of every
update_wall_time() call, resetting last_warning and other statuses.

Fix rate limiting by using the shadow_timekeeper for
timekeeping_check_update().

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Miroslav Lichvar 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Cc: Stephen Boyd 
Fixes: commit 57d05a93ada7 ("time: Rework debugging variables so they aren't global")
Signed-off-by: Stafford Horne 
Signed-off-by: John Stultz

time: Add warning about imminent deprecation of CONFIG_GENERIC_TIME_VSYSCALL_OLD

2017-06-21T05:14:10+00:00

CONFIG_GENERIC_TIME_VSYSCALL_OLD was introduced five years ago
to allow a transition from the old vsyscall implementations to
the new method (which simplified internal accounting and made
timekeeping more precise).

However, PPC and IA64 have yet to make the transition, despite
in some cases me sending test patches to try to help it along.

http://patches.linaro.org/patch/30501/
http://patches.linaro.org/patch/35412/

If its helpful, my last pass at the patches can be found here:
https://git.linaro.org/people/john.stultz/linux.git dev/oldvsyscall-cleanup

So I think its time to set a deadline and make it clear this
is going away. So this patch adds warnings about this
functionality being dropped. Likely to be in v4.15.

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Miroslav Lichvar 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Cc: Marcelo Tosatti 
Cc: Paul Mackerras 
Cc: Anton Blanchard 
Cc: Benjamin Herrenschmidt 
Cc: Tony Luck 
Cc: Michael Ellerman 
Cc: Fenghua Yu 
Signed-off-by: John Stultz

time: Clean up CLOCK_MONOTONIC_RAW time handling

2017-06-21T05:13:59+00:00

Now that we fixed the sub-ns handling for CLOCK_MONOTONIC_RAW,
remove the duplicitive tk->raw_time.tv_nsec, which can be
stored in tk->tkr_raw.xtime_nsec (similarly to how its handled
for monotonic time).

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Miroslav Lichvar 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Cc: Stephen Boyd 
Cc: Kevin Brodsky 
Cc: Will Deacon 
Cc: Daniel Mentz 
Tested-by: Daniel Mentz 
Signed-off-by: John Stultz