Date: Thu, 28 Feb 2019 14:23:26 -0800 From: Mark Millard <marklmi@yahoo.com> To: Konstantin Belousov <kib@freebsd.org> Cc: freebsd-hackers Hackers <freebsd-hackers@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: powerpc64 head -r344018 stuck sleeping problems: th->th_scale * tc_delta(th) overflows unsigned 64 bits sometimes Message-ID: <5C2FABEC-C56A-4153-A3FD-D5E1D54F1F6E@yahoo.com> In-Reply-To: <C42A56E5-63C8-41DC-B298-B43BFFB66064@yahoo.com> References: <D3D7E9F4-9A5E-4320-B3C8-EC5CEF4A2764@yahoo.com> <20190228145542.GT2420@kib.kiev.ua> <20190228150811.GU2420@kib.kiev.ua> <0A345E1F-7675-4B4B-8A74-ACD59E90E72F@yahoo.com> <C42A56E5-63C8-41DC-B298-B43BFFB66064@yahoo.com>
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[I was distracted and made a stupid mistake. Sorry for
the noise.]
On 2019-Feb-28, at 13:50, Mark Millard <marklmi@yahoo.com> wrote:
> [I left implicit that I was summarizing for x!=3D0.]
>=20
> On 2019-Feb-28, at 13:46, Mark Millard <marklmi at yahoo.com> wrote:
>=20
>=20
>=20
>> On 2019-Feb-28, at 07:08, Konstantin Belousov <kib at freebsd.org> =
wrote:
>>=20
>>> On Thu, Feb 28, 2019 at 04:55:42PM +0200, Konstantin Belousov wrote:
>>>> On Thu, Feb 28, 2019 at 05:06:23AM -0800, Mark Millard via =
freebsd-ppc wrote:
>>>>> . . .
>>>>=20
>>>> . . .
>>>=20
>>> Of course I botched the formula, please try this instead:
>>>=20
>>> diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
>>> index 2656fb4d22f..fdd4f4f6a52 100644
>>> --- a/sys/kern/kern_tc.c
>>> +++ b/sys/kern/kern_tc.c
>>> @@ -355,13 +355,22 @@ void
>>> binuptime(struct bintime *bt)
>>> {
>>> struct timehands *th;
>>> - u_int gen;
>>> + uint64_t scale, x;
>>> + u_int delta, gen;
>>>=20
>>> do {
>>> th =3D timehands;
>>> gen =3D atomic_load_acq_int(&th->th_generation);
>>> *bt =3D th->th_offset;
>>> - bintime_addx(bt, th->th_scale * tc_delta(th));
>>> + scale =3D th->th_scale;
>>> + delta =3D tc_delta(th);
>>> + if (fls(scale) + fls(delta) > 63) {
>>> + x =3D (scale >> 32) * delta;
>>> + scale &=3D UINT_MAX;
>>=20
>> The following two lines confuse me overall:
>>=20
>>> + bt->sec +=3D x >> 32;
>>> + bintime_addx(bt, x << 32);
>>=20
>> bintime_addx does:
>>=20
>> static __inline void
>> bintime_addx(struct bintime *_bt, uint64_t _x)
>> {
>> uint64_t _u;
>>=20
>> _u =3D _bt->frac;
>> _bt->frac +=3D _x;
>> if (_u > _bt->frac)
>> _bt->sec++;
>> }
>>=20
>> So I'd expect:
>=20
> I forgot to indicate the context: when x!-0
>=20
>> bintime_addx(bt, x << 32)
>>=20
>> to find _u > _bt->frac and to also do _bt->sec++ .
>> So overall (as a means of summarizing for
>> bt->sec):
How I got _u > _bt->frac for that call in general
when the call's (x<<32) !=3D 0 I do not know.
So ignore my stupid, mistaken questions.
>> bt->sec +=3D (x >> 32) + 1;
>>=20
>> Is that the intent?
>>=20
>>=20
>>> + }
>>> + bintime_addx(bt, scale * delta);
>>> atomic_thread_fence_acq();
>>> } while (gen =3D=3D 0 || gen !=3D th->th_generation);
>>> }
>>> @@ -388,13 +397,22 @@ void
>>> bintime(struct bintime *bt)
>>> {
>>> struct timehands *th;
>>> - u_int gen;
>>> + uint64_t scale, x;
>>> + u_int delta, gen;
>>>=20
>>> do {
>>> th =3D timehands;
>>> gen =3D atomic_load_acq_int(&th->th_generation);
>>> *bt =3D th->th_bintime;
>>> - bintime_addx(bt, th->th_scale * tc_delta(th));
>>> + scale =3D th->th_scale;
>>> + delta =3D tc_delta(th);
>>> + if (fls(scale) + fls(delta) > 63) {
>>> + x =3D (scale >> 32) * delta;
>>> + scale &=3D UINT_MAX;
>>=20
>> The same for the below two lines:
>>=20
>>> + bt->sec +=3D x >> 32;
>>> + bintime_addx(bt, x << 32);
>>=20
>>=20
>>> + }
>>> + bintime_addx(bt, scale * delta);
>>> atomic_thread_fence_acq();
>>> } while (gen =3D=3D 0 || gen !=3D th->th_generation);
>>> }
>>=20
>=20
>=20
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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