linux.git/kernel/time/hrtimer.c, branch v4.4.114

hrtimer: Reset hrtimer cpu base proper on CPU hotplug

2018-01-31T11:06:12+00:00

commit d5421ea43d30701e03cadc56a38854c36a8b4433 upstream.

The hrtimer interrupt code contains a hang detection and mitigation
mechanism, which prevents that a long delayed hrtimer interrupt causes a
continous retriggering of interrupts which prevent the system from making
progress. If a hang is detected then the timer hardware is programmed with
a certain delay into the future and a flag is set in the hrtimer cpu base
which prevents newly enqueued timers from reprogramming the timer hardware
prior to the chosen delay. The subsequent hrtimer interrupt after the delay
clears the flag and resumes normal operation.

If such a hang happens in the last hrtimer interrupt before a CPU is
unplugged then the hang_detected flag is set and stays that way when the
CPU is plugged in again. At that point the timer hardware is not armed and
it cannot be armed because the hang_detected flag is still active, so
nothing clears that flag. As a consequence the CPU does not receive hrtimer
interrupts and no timers expire on that CPU which results in RCU stalls and
other malfunctions.

Clear the flag along with some other less critical members of the hrtimer
cpu base to ensure starting from a clean state when a CPU is plugged in.

Thanks to Paul, Sebastian and Anna-Maria for their help to get down to the
root cause of that hard to reproduce heisenbug. Once understood it's
trivial and certainly justifies a brown paperbag.

Fixes: 41d2e4949377 ("hrtimer: Tune hrtimer_interrupt hang logic")
Reported-by: Paul E. McKenney 
Signed-off-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Sebastian Sewior 
Cc: Anna-Maria Gleixner 
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801261447590.2067@nanos
Signed-off-by: Greg Kroah-Hartman

time: Avoid undefined behaviour in ktime_add_safe()

2018-01-31T11:06:08+00:00

commit 979515c5645830465739254abc1b1648ada41518 upstream.

I ran into this:

    ================================================================================
    UBSAN: Undefined behaviour in kernel/time/hrtimer.c:310:16
    signed integer overflow:
    9223372036854775807 + 50000 cannot be represented in type 'long long int'
    CPU: 2 PID: 4798 Comm: trinity-c2 Not tainted 4.8.0-rc1+ #91
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014
     0000000000000000 ffff88010ce6fb88 ffffffff82344740 0000000041b58ab3
     ffffffff84f97a20 ffffffff82344694 ffff88010ce6fbb0 ffff88010ce6fb60
     000000000000c350 ffff88010ce6f968 dffffc0000000000 ffffffff857bc320
    Call Trace:
     [] dump_stack+0xac/0xfc
     [] ? _atomic_dec_and_lock+0xc4/0xc4
     [] ubsan_epilogue+0xd/0x8a
     [] handle_overflow+0x202/0x23d
     [] ? val_to_string.constprop.6+0x11e/0x11e
     [] ? timerqueue_add+0x151/0x410
     [] ? hrtimer_start_range_ns+0x3b8/0x1380
     [] ? memset+0x31/0x40
     [] __ubsan_handle_add_overflow+0xe/0x10
     [] hrtimer_nanosleep+0x5d9/0x790
     [] ? hrtimer_init_sleeper+0x80/0x80
     [] ? __might_sleep+0x5b/0x260
     [] common_nsleep+0x20/0x30
     [] SyS_clock_nanosleep+0x197/0x210
     [] ? SyS_clock_getres+0x150/0x150
     [] ? __this_cpu_preempt_check+0x13/0x20
     [] ? __context_tracking_exit.part.3+0x30/0x1b0
     [] ? SyS_clock_getres+0x150/0x150
     [] do_syscall_64+0x1b3/0x4b0
     [] entry_SYSCALL64_slow_path+0x25/0x25
    ================================================================================

Add a new ktime_add_unsafe() helper which doesn't check for overflow, but
doesn't throw a UBSAN warning when it does overflow either.

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Signed-off-by: Vegard Nossum 
Signed-off-by: John Stultz 
Signed-off-by: Jiri Slaby 
Signed-off-by: Greg Kroah-Hartman

hrtimer: Catch illegal clockids

2016-09-15T06:27:44+00:00

[ Upstream commit 9006a01829a50cfd6bbd4980910ed46e895e93d7 ]

It is way too easy to take any random clockid and feed it to
the hrtimer subsystem. At best, it gets mapped to a monotonic
base, but it would be better to just catch illegal values as
early as possible.

This patch does exactly that, mapping illegal clockids to an
illegal base index, and panicing when we detect the illegal
condition.

Signed-off-by: Marc Zyngier 
Cc: Tomasz Nowicki 
Cc: Christoffer Dall 
Link: http://lkml.kernel.org/r/1452879670-16133-3-git-send-email-marc.zyngier@arm.com
Signed-off-by: Thomas Gleixner 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

hrtimer: Handle remaining time proper for TIME_LOW_RES

2016-02-17T20:30:57+00:00

commit 203cbf77de59fc8f13502dcfd11350c6d4a5c95f upstream.

If CONFIG_TIME_LOW_RES is enabled we add a jiffie to the relative timeout to
prevent short sleeps, but we do not account for that in interfaces which
retrieve the remaining time.

Helge observed that timerfd can return a remaining time larger than the
relative timeout. That's not expected and breaks userland test programs.

Store the information that the timer was armed relative and provide functions
to adjust the remaining time. To avoid bloating the hrtimer struct make state
a u8, which as a bonus results in better code on x86 at least.

Reported-and-tested-by: Helge Deller 
Signed-off-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: John Stultz 
Cc: linux-m68k@lists.linux-m68k.org
Cc: dhowells@redhat.com
Link: http://lkml.kernel.org/r/20160114164159.273328486@linutronix.de
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

time: Fix spelling in comments

2015-09-22T10:54:23+00:00

Signed-off-by: Zhen Lei 
Cc: Hanjun Guo 
Cc: John Stultz 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Rafael J. Wysocki 
Cc: Thomas Gleixner 
Cc: Tianhong Ding 
Cc: Viresh Kumar 
Cc: Xinwei Hu 
Cc: Xunlei Pang 
Cc: Zefan Li 
Link: http://lkml.kernel.org/r/1440484973-13892-1-git-send-email-thunder.leizhen@huawei.com
[ Fixed yet another typo in one of the sentences fixed. ]
Signed-off-by: Ingo Molnar

hrtimer: Handle failure of tick_init_highres() gracefully

2015-08-22T08:57:50+00:00

Commit 75e3b37d0598 ("hrtimer: Drop return code of hrtimer_switch_to_hres()")
drops the return code of hrtimer_switch_to_hres(). While doing so, it also
drops the return statement itself on failure. This may cause a system hang.
Seen when running arm:multi_v7_defconfig in qemu with devicetree file
vexpress-v2p-ca9.

Fixes: 75e3b37d0598 ("hrtimer: Drop return code of hrtimer_switch_to_hres()")
Cc: Luiz Capitulino 
Signed-off-by: Guenter Roeck 
Link: http://lkml.kernel.org/r/1440231047-16256-1-git-send-email-linux@roeck-us.net
Signed-off-by: Thomas Gleixner

hrtimer: Unconfuse switch_hrtimer_base() a bit

2015-08-18T16:36:59+00:00

The variable called "this_base" is confusing because its name suggests
it's of "struct hrtimer_clock_base" type, along with "base" and "new_base"
which doesn't help understanding this complicated function.

Make its name clearer and fix the misleading comment while at it.

[ tglx: Fixed the comment for real ]

Signed-off-by: Frederic Weisbecker 
Link: http://lkml.kernel.org/r/1439907509-9553-3-git-send-email-fweisbec@gmail.com
Signed-off-by: Thomas Gleixner

hrtimer: Simplify get_target_base() by returning current base

2015-08-18T16:36:59+00:00

Instead of fetching again the current cpu base, just take it from the
parameter.

Signed-off-by: Frederic Weisbecker 
Link: http://lkml.kernel.org/r/1439907509-9553-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Thomas Gleixner

hrtimer: Drop return code of hrtimer_switch_to_hres()

2015-08-17T21:19:03+00:00

It's not checked by the caller.

Signed-off-by: Luiz Capitulino 
Link: http://lkml.kernel.org/r/20150811164043.538241ef@redhat.com
Signed-off-by: Thomas Gleixner

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

2015-06-23T01:57:44+00:00

Pull timer updates from Thomas Gleixner:
 "A rather largish update for everything time and timer related:

   - Cache footprint optimizations for both hrtimers and timer wheel

   - Lower the NOHZ impact on systems which have NOHZ or timer migration
     disabled at runtime.

   - Optimize run time overhead of hrtimer interrupt by making the clock
     offset updates smarter

   - hrtimer cleanups and removal of restrictions to tackle some
     problems in sched/perf

   - Some more leap second tweaks

   - Another round of changes addressing the 2038 problem

   - First step to change the internals of clock event devices by
     introducing the necessary infrastructure

   - Allow constant folding for usecs/msecs_to_jiffies()

   - The usual pile of clockevent/clocksource driver updates

  The hrtimer changes contain updates to sched, perf and x86 as they
  depend on them plus changes all over the tree to cleanup API changes
  and redundant code, which got copied all over the place.  The y2038
  changes touch s390 to remove the last non 2038 safe code related to
  boot/persistant clock"

* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (114 commits)
  clocksource: Increase dependencies of timer-stm32 to limit build wreckage
  timer: Minimize nohz off overhead
  timer: Reduce timer migration overhead if disabled
  timer: Stats: Simplify the flags handling
  timer: Replace timer base by a cpu index
  timer: Use hlist for the timer wheel hash buckets
  timer: Remove FIFO "guarantee"
  timers: Sanitize catchup_timer_jiffies() usage
  hrtimer: Allow hrtimer::function() to free the timer
  seqcount: Introduce raw_write_seqcount_barrier()
  seqcount: Rename write_seqcount_barrier()
  hrtimer: Fix hrtimer_is_queued() hole
  hrtimer: Remove HRTIMER_STATE_MIGRATE
  selftest: Timers: Avoid signal deadlock in leap-a-day
  timekeeping: Copy the shadow-timekeeper over the real timekeeper last
  clockevents: Check state instead of mode in suspend/resume path
  selftests: timers: Add leap-second timer edge testing to leap-a-day.c
  ntp: Do leapsecond adjustment in adjtimex read path
  time: Prevent early expiry of hrtimers[CLOCK_REALTIME] at the leap second edge
  ntp: Introduce and use SECS_PER_DAY macro instead of 86400
  ...