I ran into this:
================================================================================
UBSAN: Undefined behaviour in kernel/time/time.c:783:2
signed integer overflow:
5273 + 9223372036854771711 cannot be represented in type 'long int'
CPU: 0 PID: 17363 Comm: trinity-c0 Not tainted 4.8.0-rc1+ #88
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org
04/01/2014
0000000000000000 ffff88011457f8f0 ffffffff82344f50 0000000041b58ab3
ffffffff84f98080 ffffffff82344ea4 ffff88011457f918 ffff88011457f8c8
ffff88011457f8e0 7fffffffffffefff ffff88011457f6d8 dffffc0000000000
Call Trace:
[<ffffffff82344f50>] dump_stack+0xac/0xfc
[<ffffffff82344ea4>] ? _atomic_dec_and_lock+0xc4/0xc4
[<ffffffff8242f4c8>] ubsan_epilogue+0xd/0x8a
[<ffffffff8242fc04>] handle_overflow+0x202/0x23d
[<ffffffff8242fa02>] ? val_to_string.constprop.6+0x11e/0x11e
[<ffffffff823c7837>] ? debug_smp_processor_id+0x17/0x20
[<ffffffff8131b581>] ? __sigqueue_free.part.13+0x51/0x70
[<ffffffff8146d4e0>] ? rcu_is_watching+0x110/0x110
[<ffffffff8242fc4d>] __ubsan_handle_add_overflow+0xe/0x10
[<ffffffff81476ef8>] timespec64_add_safe+0x298/0x340
[<ffffffff81476c60>] ? timespec_add_safe+0x330/0x330
[<ffffffff812f7990>] ? wait_noreap_copyout+0x1d0/0x1d0
[<ffffffff8184bf18>] poll_select_set_timeout+0xf8/0x170
[<ffffffff8184be20>] ? poll_schedule_timeout+0x2b0/0x2b0
[<ffffffff813aa9bb>] ? __might_sleep+0x5b/0x260
[<ffffffff833c8a87>] __sys_recvmmsg+0x107/0x790
[<ffffffff833c8980>] ? SyS_recvmsg+0x20/0x20
[<ffffffff81486378>] ? hrtimer_start_range_ns+0x3b8/0x1380
[<ffffffff845f8bfb>] ? _raw_spin_unlock_irqrestore+0x3b/0x60
[<ffffffff8148bcea>] ? do_setitimer+0x39a/0x8e0
[<ffffffff813aa9bb>] ? __might_sleep+0x5b/0x260
[<ffffffff833c9110>] ? __sys_recvmmsg+0x790/0x790
[<ffffffff833c91e9>] SyS_recvmmsg+0xd9/0x160
[<ffffffff833c9110>] ? __sys_recvmmsg+0x790/0x790
[<ffffffff823c7853>] ? __this_cpu_preempt_check+0x13/0x20
[<ffffffff8162f680>] ? __context_tracking_exit.part.3+0x30/0x1b0
[<ffffffff833c9110>] ? __sys_recvmmsg+0x790/0x790
[<ffffffff81007bd3>] do_syscall_64+0x1b3/0x4b0
[<ffffffff845f936a>] entry_SYSCALL64_slow_path+0x25/0x25
================================================================================
Line 783 is this:
783 set_normalized_timespec64(&res, lhs.tv_sec + rhs.tv_sec,
784 lhs.tv_nsec + rhs.tv_nsec);
In other words, since lhs.tv_sec and rhs.tv_sec are both time64_t, this
is a signed addition which will cause undefined behaviour on overflow.
Note that this is not currently a huge concern since the kernel should be
built with -fno-strict-overflow by default, but could be a problem in the
future, a problem with older compilers, or other compilers than gcc.
The easiest way to avoid the overflow is to cast one of the arguments to
unsigned (so the addition will be done using unsigned arithmetic).
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
All references to timespec_add_safe() now use timespec64_add_safe().
The plan is to replace struct timespec references with struct timespec64
throughout the kernel as timespec is not y2038 safe.
Drop timespec_add_safe() and use timespec64_add_safe() for all
architectures.
Link: http://lkml.kernel.org/r/1461947989-21926-4-git-send-email-deepa.kernel@gmail.com
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
timespec64_add_safe() has been defined in time64.h for 64 bit systems.
But, 32 bit systems only have an extern function prototype defined.
Provide a definition for the above function.
The function will be necessary as part of y2038 changes. struct
timespec is not y2038 safe. All references to timespec will be replaced
by struct timespec64. The function is meant to be a replacement for
timespec_add_safe().
The implementation is similar to timespec_add_safe().
Link: http://lkml.kernel.org/r/1461947989-21926-2-git-send-email-deepa.kernel@gmail.com
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The struct itimerspec is not year 2038 safe on 32bit systems due to
the limitation of the struct timespec members. Introduce itimerspec64
which uses struct timespec64 instead and provide conversion functions.
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Currently, leapsecond adjustments are done at tick time. As a result,
the leapsecond was applied at the first timer tick *after* the
leapsecond (~1-10ms late depending on HZ), rather then exactly on the
second edge.
This was in part historical from back when we were always tick based,
but correcting this since has been avoided since it adds extra
conditional checks in the gettime fastpath, which has performance
overhead.
However, it was recently pointed out that ABS_TIME CLOCK_REALTIME
timers set for right after the leapsecond could fire a second early,
since some timers may be expired before we trigger the timekeeping
timer, which then applies the leapsecond.
This isn't quite as bad as it sounds, since behaviorally it is similar
to what is possible w/ ntpd made leapsecond adjustments done w/o using
the kernel discipline. Where due to latencies, timers may fire just
prior to the settimeofday call. (Also, one should note that all
applications using CLOCK_REALTIME timers should always be careful,
since they are prone to quirks from settimeofday() disturbances.)
However, the purpose of having the kernel do the leap adjustment is to
avoid such latencies, so I think this is worth fixing.
So in order to properly keep those timers from firing a second early,
this patch modifies the ntp and timekeeping logic so that we keep
enough state so that the update_base_offsets_now accessor, which
provides the hrtimer core the current time, can check and apply the
leapsecond adjustment on the second edge. This prevents the hrtimer
core from expiring timers too early.
This patch does not modify any other time read path, so no additional
overhead is incurred. However, this also means that the leap-second
continues to be applied at tick time for all other read-paths.
Apologies to Richard Cochran, who pushed for similar changes years
ago, which I resisted due to the concerns about the performance
overhead.
While I suspect this isn't extremely critical, folks who care about
strict leap-second correctness will likely want to watch
this. Potentially a -stable candidate eventually.
Originally-suggested-by: Richard Cochran <richardcochran@gmail.com>
Reported-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Reported-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1434063297-28657-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
On 32-bit systems, timespec64_add_ns() calls __iter_div_u64_rem()
which needs math64.h, and we want to include time64.h in some
cases.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Helper and conversion functions for timespec64.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Define the timespec64 structure and standard helper functions.
[ tglx: Make it 32bit only. 64bit really can map timespec to timespec64 ]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
