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Groups > linux.kernel > #1312549
| From | Jeff Merkey <linux.mdb@gmail.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup |
| Date | 2016-01-19 23:10 +0100 |
| Message-ID | <qSMDo-5wa-25@gated-at.bofh.it> (permalink) |
| References | <qStKq-Kn-15@gated-at.bofh.it> <qSGxX-1lu-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Nasty bug but trivial fix for this. What happens here is RAX (nsecs)
gets set to a huge value (RAX = 0x17AE7F57C671EA7D) and passed through
a bunch of macros to __iter_div_u64_rem(). It doesn't loop infinitely
with a number that big, just for about 4 minutes but long enough for
the hard lockup detector to fire off. Setting RAX=0 when this bug
occurs clears the problem from the debugger console when this function
gets stuck in this loop and the system recovers fine.
The problem code is in:
include/linux/math64.h:117
static __always_inline u32
__iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
{
u32 ret = 0;
while (dividend >= divisor) {
/* The following asm() prevents the compiler from
optimising this loop into a modulo operation. */
asm("" : "+rm"(dividend));
dividend -= divisor;
ret++;
}
*remainder = dividend;
return ret;
}
which is called by
include/linux/time.h:233
static __always_inline void timespec_add_ns(struct timespec *a, u64 ns)
{
a->tv_sec += __iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
a->tv_nsec = ns;
}
it's defined so that timespec64_add_ns just points to this function
which is called by ktime_get_ts64. tv_nsec + ns gets passed as a huge
number (RAX = 0x17AE7F57C671EA7D) with a very small divisor and just
sits there and loops.
Submitting a patch to fix this after I regress and test it. Since it
makes no sense to loop on a simple calculation, fix should be:
static __always_inline void timespec_add_ns(struct timespec *a, u64 ns)
{
a->tv_sec += div64_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
a->tv_nsec = ns;
}
Jeff
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-19 03:00 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-19 03:20 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-19 03:40 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Thomas Gleixner <tglx@linutronix.de> - 2016-01-19 11:00 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-19 16:40 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-19 23:10 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 02:00 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Thomas Gleixner <tglx@linutronix.de> - 2016-01-20 10:30 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Thomas Gleixner <tglx@linutronix.de> - 2016-01-20 15:30 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 17:50 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 18:00 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 18:20 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 18:40 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup John Stultz <john.stultz@linaro.org> - 2016-01-20 18:40 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Thomas Gleixner <tglx@linutronix.de> - 2016-01-20 18:50 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup John Stultz <john.stultz@linaro.org> - 2016-01-20 19:00 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 19:10 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Thomas Gleixner <tglx@linutronix.de> - 2016-01-20 18:30 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 18:40 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Thomas Gleixner <tglx@linutronix.de> - 2016-01-20 20:40 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-20 21:10 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-21 08:20 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-21 09:20 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-21 10:10 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Thomas Gleixner <tglx@linutronix.de> - 2016-01-21 11:20 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-21 16:50 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-21 18:00 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-21 18:10 +0100
Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup Jeff Merkey <linux.mdb@gmail.com> - 2016-01-21 18:10 +0100
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