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To: Sergey Kaplun <skaplun@tarantool.org>
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Subject: Re: [Tarantool-patches] [PATCH luajit] ARM64: Fix write barrier in
BC_USETS.
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From: Sergey Ostanevich via Tarantool-patches
<tarantool-patches@dev.tarantool.org>
Reply-To: Sergey Ostanevich <sergos@tarantool.org>
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Hi!
Thanks for the patch, LGTM.
I have no other explanation than that =E2=80=98missed flag as a result =
of compare=E2=80=99.
But you did it better - took time for me to get to the point.=20
BTW, will make easier to grasp with a simple C equivalent, like=20
- if (iswite(str) || closed !=3D 0)
+ if (iswite(str) || closed =3D=3D 0)
Sergos.
> On 9 Aug 2021, at 19:01, Sergey Kaplun <skaplun@tarantool.org> wrote:
>=20
> Igor, thanks for the feedback!
>=20
> On 08.08.21, Igor Munkin wrote:
>> Sergey,
>>=20
>> Thanks for the fixes! See some new comments below.
>>=20
>> On 01.08.21, Sergey Kaplun wrote:
>>> Igor,
>>>=20
>>> Thanks for the review!
>>> Update commit message on the branch, considering you comments.
>>=20
>> Got it, but I still have some more comments regarding it.
>>=20
>>>=20
>>> See answers to you questions below.
>>>=20
>>=20
>> <snipped>
>>=20
>>>=20
>>>>=20
>>>>> | ccmp TMP0w, #0, #0, ne
>>>>> | beq <1 // branch out from barrier movement
>>>>> `TMP0w` contains `upvalue->closed` field. If it equals NULL (the =
first
>>>>> `#0`). The second zero is the value of NZCV condition flags set if =
the
>>>>> condition (`ne`) is FALSE [1][2]. If the set value is not white, =
then
>>>>> flags are set to zero and branch is not taken (no Zero flag). If =
it
>>>>> happens at propagate or atomic GC State and the =
`lj_gc_barrieruv()`
>>>>> function is called then the gray value to set is marked as white. =
That
>>>>> leads to the assertion failure in the `gc_mark()` function.
>>>>=20
>>>> OK, I understand almost nothing from the part above. Here are the
>>>> comments:
>>>> 1. "If it equals NULL (the first `#0`)", then what?
>>>=20
>>> My bad:
>>> I mean here:
>>> If it equals NULL (the first `#0`), then the upvalue is open.
>>=20
>> So why do you use NULL instead of 0? The field is uint8_t type, so 0 =
is
>> much clearer.
>=20
> Changed.
>=20
>>=20
>>> Added this.
>>>=20
>>>> 2. Just to check we are on the same page: the second "immediate"
>>>> mentioned in docs[1] is NZCV?
>>>=20
>>> Yes.
>>>=20
>>>> Then beq <1 branch is not taken since
>>>> (TMP0w !=3D 0) is FALSE (i.e. upvalue is not closed), but zero flag =
in
>>>> NZCV value is not set?
>>>=20
>>> Yes.
>>>=20
>>>> So how does the color of the value to be =
stored
>>>> relate to this control flow?
>>>=20
>>> This NZCV value isn't set if the upvalue is white, because condition =
is
>>> of the following instruction
>>>=20
>>> | tst TMP1w, #LJ_GC_WHITES // iswhite(str)
>>>=20
>>> is TRUE. So the <1 branch is taken, because the upvalue is closed.
>>=20
>> Well... I can't imagine how I needed to find this... This relates =
mostly
>> to ARM docs you've mentioned, but it would be nice to describe this
>> behaviour in the commit message (since you're writing a verbose one).
>>=20
>>>=20
>>>> 3. AFAICS, if the branch is not taken and <lj_gc_barrieruv> is =
called at
>>>> propagate or atomic phase, the value is colored either to gray or =
black.
>>>=20
>>> Yes, that leads to the assertion failure mentioned in the ticket in =
the
>>> LuaJIT upstream.
>>>=20
>>>>=20
>>>>>=20
>>>>> This patch changes yielded NZCV condition flag to 4 (Zero flag is =
up) to
>>>>> take the correct branch after `ccmp` instruction.
>>>>>=20
>>>>> Sergey Kaplun:
>>>>> * added the description and the test for the problem
>>>>>=20
>>>>> [1]: =
https://developer.arm.com/documentation/dui0801/g/pge1427897656225
>>>>> [2]: =
https://community.arm.com/developer/ip-products/processors/b/processors-ip=
-blog/posts/condition-codes-1-condition-flags-and-codes
>>>>=20
>>>> Minor: Why #5629 is not mentioned?
>>>=20
>>> Added.
>>=20
>> Considering everything above, I propose the following wording:
>> | Contributed by Javier Guerra Giraldez.
>> |
>> | (cherry picked from commit =
c785131ca5a6d24adc519e5e0bf1b69b671d912f)
>> |
>> |
>> | Closed upvalues are never gray. Hence when closed upvalue is =
marked, it
>> | is marked as black. Black objects can't refer white objects, so for
>> | storing a white value in a closed upvalue, we need to move the =
barrier
>> | forward and color our value to gray by using `lj_gc_barrieruv()`. =
This
>> | function can't be called on closed upvalues with non-white values =
since
>> | there is no need to mark it again.
>> |
>> | USETS bytecode for arm64 architecture has the incorrect NZCV =
condition
>> | flag value in the instruction that checks the upvalue is closed:
>> | | tst TMP1w, #LJ_GC_WHITES
>> | | ccmp TMP0w, #0, #0, ne
>> | | beq <1 // branch out from barrier movement
>> | `TMP0w` contains `upvalue->closed` field, so the upvalue is open if =
this
>> | field equals to zero (the first one in `ccmp`). The second zero is =
the
>> | value of NZCV condition flags[1] yielded if the specified condition
>> | (`ne`) is met for the current values of the condition flags[2]. =
Hence,
>> | if the value to be stored is not white (`TMP1w` holds its color), =
then
>> | the condition is FALSE and all flags bits are set to zero so branch =
is
>> | not taken (Zero flag is not set). If this happens at propagate or =
atomic
>> | GC phase, the `lj_gc_barrieruv()` function is called and the gray =
value
>> | to be set is marked like if it is white. That leads to the =
assertion
>> | failure in the `gc_mark()` function.
>> |
>> | This patch changes NZCV condition flag to 4 (Zero flag is set) to =
take
>> | the correct branch after `ccmp` instruction.
>> |
>> | Sergey Kaplun:
>> | * added the description and the test for the problem
>> |
>> | [1]: =
https://community.arm.com/developer/ip-products/processors/b/processors-ip=
-blog/posts/condition-codes-1-condition-flags-and-codes
>> | [2]: =
https://developer.arm.com/documentation/dui0801/g/pge1427897656225
>> |
>> | Part of tarantool/tarantool#5629
>=20
> Updated, as you've suggested.
>=20
>>=20
>>>=20
>>=20
>> <snipped>
>>=20
>>>>=20
>>>>>=20
>>>>> src/vm_arm64.dasc | 2 +-
>>>>> ...6-arm64-incorrect-check-closed-uv.test.lua | 38 =
+++++++++++++++++++
>>>>> 2 files changed, 39 insertions(+), 1 deletion(-)
>>>>> create mode 100644 =
test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua
>>>>>=20
>>>>=20
>>>> <snipped>
>>>>=20
>>>>> diff --git =
a/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua
>>>>> new file mode 100644
>>>>> index 00000000..b757133f
>>>>> --- /dev/null
>>>>> +++ =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua
>>>>> @@ -0,0 +1,38 @@
>>>>> +local tap =3D require('tap')
>>>>> +
>>>>> +local test =3D tap.test('lj-426-arm64-incorrect-check-closed-uv')
>>>>> +test:plan(1)
>>>>> +
>>>>> +-- Test file to demonstrate LuaJIT USETS bytecode incorrect
>>>>> +-- behaviour on arm64 in case when non-white object is set to
>>>>> +-- closed upvalue.
>>>>> +-- See also, https://github.com/LuaJIT/LuaJIT/issues/426.
>>>>> +
>>>>> +-- First, create a closed upvalue.
>>>>> +do
>>>>=20
>>>> Minor: I'm not sure, we need a separate lexical block here. Could =
you
>>>> please clarify the reason in the comment?
>>>=20
>>> We need a closed upvalue. I suppose that it is the simpiest way to
>>> create one. Please, provide a simplier example if you know one.
>>=20
>> My bad. Yes, the easiest way to emit UCLO bytecode is using a =
separate
>> lexical block.
>>=20
>>>=20
>>>>=20
>>>>> + local uv -- luacheck: no unused
>>>>> + -- The function's prototype is created with the following
>>>>> + -- constants at chunk parsing. After adding this constant to
>>>>> + -- the function's prototype it will be marked as gray during
>>>>> + -- propogate phase.
>>>>=20
>>>> Then what does it test, if the constant is marked as gray? Will =
this
>>>> string be white later?
>>>=20
>>> It shouldn't be white, it should be gray, otherwise the =
aforementioned
>>> condition is TRUE (remember, we need FALSE).
>>=20
>> Again, PEBKAC, thanks for the explanation.
>>=20
>>>=20
>>>>=20
>>>>> + local function usets() uv =3D '' end
>>>>> + _G.usets =3D usets
>>>>> +end
>>>>> +
>>>>> +-- Set GC state to GCpause.
>>>>> +collectgarbage()
>>>>> +-- Do GC step as often as possible.
>>>>> +collectgarbage('setstepmul', 100)
>>>>=20
>>>> Minor: Don't get, why you need to make GC less aggressive for the =
test.
>>>> The test is run, until propagate phase is finished.
>>>=20
>>> More likely, that it is run, until the upvalue is marked as black
>>> during traversing (with the bug). I can remove this line if you =
insist.
>>=20
>> Drop it, please. I can't even *feel* its effect ;)
>=20
> Done.
>=20
>>=20
>>>=20
>>>>=20
>>>>> +
>>>>> +-- We don't know on what exactly step our upvalue is marked as
>>>>> +-- black and USETS become dangerous, so just check it at each
>>>>> +-- step.
>>>>> +-- Don't need to do the full GC cycle step by step.
>>=20
>> Minor: It would be nice to drop a few words about string and upvalue
>> colours during this loop, but it's up to you.
>=20
> Added.
>=20
> The iterative patch is the following:
>=20
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> diff --git =
a/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua
> index b757133f..4cdf1211 100644
> --- =
a/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua
> +++ =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua
> @@ -21,9 +21,10 @@ end
>=20
> -- Set GC state to GCpause.
> collectgarbage()
> --- Do GC step as often as possible.
> -collectgarbage('setstepmul', 100)
>=20
> +-- We want to wait for the situation, when upvalue is black,
> +-- the string is gray. Both conditions are satisfied, when the
> +-- corresponding `usets()` function is marked, for example.
> -- We don't know on what exactly step our upvalue is marked as
> -- black and USETS become dangerous, so just check it at each
> -- step.
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>=20
>>=20
>>>>> +local old_steps_atomic =3D misc.getmetrics().gc_steps_atomic
>>>>> +while (misc.getmetrics().gc_steps_atomic =3D=3D old_steps_atomic) =
do
>>>>> + collectgarbage('step')
>>>>> + usets() -- luacheck: no global
>>>>> +end
>>>>> +
>>>>> +test:ok(true)
>>>>> +os.exit(test:check() and 0 or 1)
>>>>> --=20
>>>>> 2.31.0
>>>>>=20
>>>>=20
>>>> [1]: =
https://lists.tarantool.org/tarantool-patches/20210719073632.12008-1-skapl=
un@tarantool.org/T/#u
>>>>=20
>>>> --=20
>>>> Best regards,
>>>> IM
>>>=20
>>> --=20
>>> Best regards,
>>> Sergey Kaplun
>>=20
>> --=20
>> Best regards,
>> IM
>=20
> --=20
> Best regards,
> Sergey Kaplun
--Apple-Mail=_280D9147-E72B-4DC1-9FE3-5CD77A99F455
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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html; =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;" =
class=3D"">Hi!<div class=3D""><br class=3D""></div><div class=3D"">Thanks =
for the patch, LGTM.</div><div class=3D""><br class=3D""></div><div =
class=3D"">I have no other explanation than that =E2=80=98missed flag as =
a result of compare=E2=80=99.</div><div class=3D"">But you did it better =
- took time for me to get to the point. </div><div class=3D"">BTW, =
will make easier to grasp with a simple C equivalent, =
like </div><div class=3D""><br class=3D""></div><div =
class=3D"">-<span class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span>if (iswite(str) || closed !=3D 0)</div><div class=3D"">+<span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> </span>if =
(iswite(str) || closed =3D=3D 0)</div><div class=3D""><br =
class=3D""></div><div class=3D"">Sergos.</div><div class=3D""><br =
class=3D""></div><div class=3D""><br class=3D""><div><br =
class=3D""><blockquote type=3D"cite" class=3D""><div class=3D"">On 9 Aug =
2021, at 19:01, Sergey Kaplun <<a href=3D"mailto:skaplun@tarantool.org"=
class=3D"">skaplun@tarantool.org</a>> wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D""><meta =
charset=3D"UTF-8" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); =
font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">Igor, thanks for the feedback!</span><br style=3D"caret-color: =
rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 11px; font-style: =
normal; font-variant-caps: normal; font-weight: normal; letter-spacing: =
normal; text-align: start; text-indent: 0px; text-transform: none; =
white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><br style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><span style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">On 08.08.21, Igor Munkin wrote:</span><br style=3D"caret-color:=
rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 11px; font-style: =
normal; font-variant-caps: normal; font-weight: normal; letter-spacing: =
normal; text-align: start; text-indent: 0px; text-transform: none; =
white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><blockquote type=3D"cite" =
style=3D"font-family: Menlo-Regular; font-size: 11px; font-style: =
normal; font-variant-caps: normal; font-weight: normal; letter-spacing: =
normal; orphans: auto; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; widows: auto; word-spacing: =
0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D"">Sergey,<br class=3D""><br =
class=3D"">Thanks for the fixes! See some new comments below.<br =
class=3D""><br class=3D"">On 01.08.21, Sergey Kaplun wrote:<br =
class=3D""><blockquote type=3D"cite" class=3D"">Igor,<br class=3D""><br =
class=3D"">Thanks for the review!<br class=3D"">Update commit message on =
the branch, considering you comments.<br class=3D""></blockquote><br =
class=3D"">Got it, but I still have some more comments regarding it.<br =
class=3D""><br class=3D""><blockquote type=3D"cite" class=3D""><br =
class=3D"">See answers to you questions below.<br class=3D""><br =
class=3D""></blockquote><br class=3D""><snipped><br class=3D""><br =
class=3D""><blockquote type=3D"cite" class=3D""><br class=3D""><blockquote=
type=3D"cite" class=3D""><br class=3D""><blockquote type=3D"cite" =
class=3D"">| ccmp TMP0w, #0, #0, ne<br class=3D"">| beq <1 // branch =
out from barrier movement<br class=3D"">`TMP0w` contains =
`upvalue->closed` field. If it equals NULL (the first<br =
class=3D"">`#0`). The second zero is the value of NZCV condition flags =
set if the<br class=3D"">condition (`ne`) is FALSE [1][2]. If the set =
value is not white, then<br class=3D"">flags are set to zero and branch =
is not taken (no Zero flag). If it<br class=3D"">happens at propagate or =
atomic GC State and the `lj_gc_barrieruv()`<br class=3D"">function is =
called then the gray value to set is marked as white. That<br =
class=3D"">leads to the assertion failure in the `gc_mark()` =
function.<br class=3D""></blockquote><br class=3D"">OK, I understand =
almost nothing from the part above. Here are the<br =
class=3D"">comments:<br class=3D"">1. "If it equals NULL (the first =
`#0`)", then what?<br class=3D""></blockquote><br class=3D"">My bad:<br =
class=3D"">I mean here:<br class=3D"">If it equals NULL (the first =
`#0`), then the upvalue is open.<br class=3D""></blockquote><br =
class=3D"">So why do you use NULL instead of 0? The field is uint8_t =
type, so 0 is<br class=3D"">much clearer.<br class=3D""></blockquote><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" =
class=3D"">Changed.</span><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><br style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><blockquote type=3D"cite" =
style=3D"font-family: Menlo-Regular; font-size: 11px; font-style: =
normal; font-variant-caps: normal; font-weight: normal; letter-spacing: =
normal; orphans: auto; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; widows: auto; word-spacing: =
0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><br class=3D""><blockquote =
type=3D"cite" class=3D"">Added this.<br class=3D""><br =
class=3D""><blockquote type=3D"cite" class=3D"">2. Just to check we are =
on the same page: the second "immediate"<br class=3D"">mentioned in =
docs[1] is NZCV?<br class=3D""></blockquote><br class=3D"">Yes.<br =
class=3D""><br class=3D""><blockquote type=3D"cite" =
class=3D""> &nb=
sp;  =
; Then beq <1 branch is not taken =
since<br class=3D"">(TMP0w !=3D 0) is FALSE (i.e. upvalue is not =
closed), but zero flag in<br class=3D"">NZCV value is not set?<br =
class=3D""></blockquote><br class=3D"">Yes.<br class=3D""><br =
class=3D""><blockquote type=3D"cite" =
class=3D""> &nb=
sp; So =
how does the color of the value to be stored<br class=3D"">relate to =
this control flow?<br class=3D""></blockquote><br class=3D"">This NZCV =
value isn't set if the upvalue is white, because condition is<br =
class=3D"">of the following instruction<br class=3D""><br class=3D"">| =
tst TMP1w, #LJ_GC_WHITES<span class=3D"Apple-tab-span" =
style=3D"white-space: pre;"> </span>// iswhite(str)<br class=3D""><br =
class=3D"">is TRUE. So the <1 branch is taken, because the upvalue is =
closed.<br class=3D""></blockquote><br class=3D"">Well... I can't =
imagine how I needed to find this... This relates mostly<br class=3D"">to =
ARM docs you've mentioned, but it would be nice to describe this<br =
class=3D"">behaviour in the commit message (since you're writing a =
verbose one).<br class=3D""><br class=3D""><blockquote type=3D"cite" =
class=3D""><br class=3D""><blockquote type=3D"cite" class=3D"">3. =
AFAICS, if the branch is not taken and <lj_gc_barrieruv> is called =
at<br class=3D"">propagate or atomic phase, the value is colored either =
to gray or black.<br class=3D""></blockquote><br class=3D"">Yes, that =
leads to the assertion failure mentioned in the ticket in the<br =
class=3D"">LuaJIT upstream.<br class=3D""><br class=3D""><blockquote =
type=3D"cite" class=3D""><br class=3D""><blockquote type=3D"cite" =
class=3D""><br class=3D"">This patch changes yielded NZCV condition flag =
to 4 (Zero flag is up) to<br class=3D"">take the correct branch after =
`ccmp` instruction.<br class=3D""><br class=3D"">Sergey Kaplun:<br =
class=3D"">* added the description and the test for the problem<br =
class=3D""><br class=3D"">[1]: <a =
href=3D"https://developer.arm.com/documentation/dui0801/g/pge1427897656225=
" =
class=3D"">https://developer.arm.com/documentation/dui0801/g/pge1427897656=
225</a><br class=3D"">[2]: <a =
href=3D"https://community.arm.com/developer/ip-products/processors/b/proce=
ssors-ip-blog/posts/condition-codes-1-condition-flags-and-codes" =
class=3D"">https://community.arm.com/developer/ip-products/processors/b/pr=
ocessors-ip-blog/posts/condition-codes-1-condition-flags-and-codes</a><br =
class=3D""></blockquote><br class=3D"">Minor: Why #5629 is not =
mentioned?<br class=3D""></blockquote><br class=3D"">Added.<br =
class=3D""></blockquote><br class=3D"">Considering everything above, I =
propose the following wording:<br class=3D"">| Contributed by Javier =
Guerra Giraldez.<br class=3D"">|<br class=3D"">| (cherry picked from =
commit c785131ca5a6d24adc519e5e0bf1b69b671d912f)<br class=3D"">|<br =
class=3D"">|<br class=3D"">| Closed upvalues are never gray. Hence when =
closed upvalue is marked, it<br class=3D"">| is marked as black. Black =
objects can't refer white objects, so for<br class=3D"">| storing a =
white value in a closed upvalue, we need to move the barrier<br =
class=3D"">| forward and color our value to gray by using =
`lj_gc_barrieruv()`. This<br class=3D"">| function can't be called on =
closed upvalues with non-white values since<br class=3D"">| there is no =
need to mark it again.<br class=3D"">|<br class=3D"">| USETS bytecode =
for arm64 architecture has the incorrect NZCV condition<br class=3D"">| =
flag value in the instruction that checks the upvalue is closed:<br =
class=3D"">| | tst TMP1w, #LJ_GC_WHITES<br class=3D"">| | ccmp TMP0w, =
#0, #0, ne<br class=3D"">| | beq <1 // branch out from barrier =
movement<br class=3D"">| `TMP0w` contains `upvalue->closed` field, so =
the upvalue is open if this<br class=3D"">| field equals to zero (the =
first one in `ccmp`). The second zero is the<br class=3D"">| value of =
NZCV condition flags[1] yielded if the specified condition<br class=3D"">|=
(`ne`) is met for the current values of the condition flags[2]. =
Hence,<br class=3D"">| if the value to be stored is not white (`TMP1w` =
holds its color), then<br class=3D"">| the condition is FALSE and all =
flags bits are set to zero so branch is<br class=3D"">| not taken (Zero =
flag is not set). If this happens at propagate or atomic<br class=3D"">| =
GC phase, the `lj_gc_barrieruv()` function is called and the gray =
value<br class=3D"">| to be set is marked like if it is white. That =
leads to the assertion<br class=3D"">| failure in the `gc_mark()` =
function.<br class=3D"">|<br class=3D"">| This patch changes NZCV =
condition flag to 4 (Zero flag is set) to take<br class=3D"">| the =
correct branch after `ccmp` instruction.<br class=3D"">|<br class=3D"">| =
Sergey Kaplun:<br class=3D"">| * added the description and the test for =
the problem<br class=3D"">|<br class=3D"">| [1]: <a =
href=3D"https://community.arm.com/developer/ip-products/processors/b/proce=
ssors-ip-blog/posts/condition-codes-1-condition-flags-and-codes" =
class=3D"">https://community.arm.com/developer/ip-products/processors/b/pr=
ocessors-ip-blog/posts/condition-codes-1-condition-flags-and-codes</a><br =
class=3D"">| [2]: <a =
href=3D"https://developer.arm.com/documentation/dui0801/g/pge1427897656225=
" =
class=3D"">https://developer.arm.com/documentation/dui0801/g/pge1427897656=
225</a><br class=3D"">|<br class=3D"">| Part of =
tarantool/tarantool#5629<br class=3D""></blockquote><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">Updated, as =
you've suggested.</span><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><br style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><blockquote type=3D"cite" =
style=3D"font-family: Menlo-Regular; font-size: 11px; font-style: =
normal; font-variant-caps: normal; font-weight: normal; letter-spacing: =
normal; orphans: auto; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; widows: auto; word-spacing: =
0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><br class=3D""><blockquote =
type=3D"cite" class=3D""><br class=3D""></blockquote><br =
class=3D""><snipped><br class=3D""><br class=3D""><blockquote =
type=3D"cite" class=3D""><blockquote type=3D"cite" class=3D""><br =
class=3D""><blockquote type=3D"cite" class=3D""><br =
class=3D"">src/vm_arm64.dasc =
&n=
bsp; &nbs=
p; | 2 +-<br =
class=3D"">...6-arm64-incorrect-check-closed-uv.test.lua | 38 =
+++++++++++++++++++<br class=3D"">2 files changed, 39 insertions(+), 1 =
deletion(-)<br class=3D"">create mode 100644 =
test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua<br =
class=3D""><br class=3D""></blockquote><br class=3D""><snipped><br =
class=3D""><br class=3D""><blockquote type=3D"cite" class=3D"">diff =
--git =
a/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua<br =
class=3D"">new file mode 100644<br class=3D"">index =
00000000..b757133f<br class=3D"">--- /dev/null<br class=3D"">+++ =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua<br =
class=3D"">@@ -0,0 +1,38 @@<br class=3D"">+local tap =3D =
require('tap')<br class=3D"">+<br class=3D"">+local test =3D =
tap.test('lj-426-arm64-incorrect-check-closed-uv')<br =
class=3D"">+test:plan(1)<br class=3D"">+<br class=3D"">+-- Test file to =
demonstrate LuaJIT USETS bytecode incorrect<br class=3D"">+-- behaviour =
on arm64 in case when non-white object is set to<br class=3D"">+-- =
closed upvalue.<br class=3D"">+-- See also, <a =
href=3D"https://github.com/LuaJIT/LuaJIT/issues/426" =
class=3D"">https://github.com/LuaJIT/LuaJIT/issues/426</a>.<br =
class=3D"">+<br class=3D"">+-- First, create a closed upvalue.<br =
class=3D"">+do<br class=3D""></blockquote><br class=3D"">Minor: I'm not =
sure, we need a separate lexical block here. Could you<br =
class=3D"">please clarify the reason in the comment?<br =
class=3D""></blockquote><br class=3D"">We need a closed upvalue. I =
suppose that it is the simpiest way to<br class=3D"">create one. Please, =
provide a simplier example if you know one.<br class=3D""></blockquote><br=
class=3D"">My bad. Yes, the easiest way to emit UCLO bytecode is using =
a separate<br class=3D"">lexical block.<br class=3D""><br =
class=3D""><blockquote type=3D"cite" class=3D""><br class=3D""><blockquote=
type=3D"cite" class=3D""><br class=3D""><blockquote type=3D"cite" =
class=3D"">+ local uv -- luacheck: no unused<br class=3D"">+ =
-- The function's prototype is created with the following<br =
class=3D"">+ -- constants at chunk parsing. After adding this =
constant to<br class=3D"">+ -- the function's prototype it will be =
marked as gray during<br class=3D"">+ -- propogate phase.<br =
class=3D""></blockquote><br class=3D"">Then what does it test, if the =
constant is marked as gray? Will this<br class=3D"">string be white =
later?<br class=3D""></blockquote><br class=3D"">It shouldn't be white, =
it should be gray, otherwise the aforementioned<br class=3D"">condition =
is TRUE (remember, we need FALSE).<br class=3D""></blockquote><br =
class=3D"">Again, PEBKAC, thanks for the explanation.<br class=3D""><br =
class=3D""><blockquote type=3D"cite" class=3D""><br class=3D""><blockquote=
type=3D"cite" class=3D""><br class=3D""><blockquote type=3D"cite" =
class=3D"">+ local function usets() uv =3D '' end<br class=3D"">+ =
_G.usets =3D usets<br class=3D"">+end<br class=3D"">+<br =
class=3D"">+-- Set GC state to GCpause.<br class=3D"">+collectgarbage()<br=
class=3D"">+-- Do GC step as often as possible.<br =
class=3D"">+collectgarbage('setstepmul', 100)<br =
class=3D""></blockquote><br class=3D"">Minor: Don't get, why you need to =
make GC less aggressive for the test.<br class=3D"">The test is run, =
until propagate phase is finished.<br class=3D""></blockquote><br =
class=3D"">More likely, that it is run, until the upvalue is marked as =
black<br class=3D"">during traversing (with the bug). I can remove this =
line if you insist.<br class=3D""></blockquote><br class=3D"">Drop it, =
please. I can't even *feel* its effect ;)<br class=3D""></blockquote><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">Done.</span><br=
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><blockquote type=3D"cite" style=3D"font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px; text-decoration: none;" class=3D""><br =
class=3D""><blockquote type=3D"cite" class=3D""><br class=3D""><blockquote=
type=3D"cite" class=3D""><br class=3D""><blockquote type=3D"cite" =
class=3D"">+<br class=3D"">+-- We don't know on what exactly step our =
upvalue is marked as<br class=3D"">+-- black and USETS become dangerous, =
so just check it at each<br class=3D"">+-- step.<br class=3D"">+-- Don't =
need to do the full GC cycle step by step.<br =
class=3D""></blockquote></blockquote></blockquote><br class=3D"">Minor: =
It would be nice to drop a few words about string and upvalue<br =
class=3D"">colours during this loop, but it's up to you.<br =
class=3D""></blockquote><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><span style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">Added.</span><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><br style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><span style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">The iterative patch is the following:</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" =
class=3D"">=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">diff --git =
a/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua</sp=
an><br style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">index =
b757133f..4cdf1211 100644</span><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><span style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">--- =
a/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua</sp=
an><br style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">+++ =
b/test/tarantool-tests/lj-426-arm64-incorrect-check-closed-uv.test.lua</sp=
an><br style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">@@ -21,9 =
+21,10 @@ end</span><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">-- Set GC =
state to GCpause.</span><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><span style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">collectgarbage()</span><br style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><span style=3D"caret-color: rgb(0, 0, =
0); font-family: Menlo-Regular; font-size: 11px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">--- Do GC step as often as possible.</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" =
class=3D"">-collectgarbage('setstepmul', 100)</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">+-- We want =
to wait for the situation, when upvalue is black,</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">+-- the =
string is gray. Both conditions are satisfied, when the</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">+-- =
corresponding `usets()` function is marked, for example.</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">-- We don't =
know on what exactly step our upvalue is marked as</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">-- black and =
USETS become dangerous, so just check it at each</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">-- =
step.</span><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" =
class=3D"">=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><blockquote type=3D"cite" style=3D"font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px; text-decoration: none;" class=3D""><br =
class=3D""><blockquote type=3D"cite" class=3D""><blockquote type=3D"cite" =
class=3D""><blockquote type=3D"cite" class=3D"">+local old_steps_atomic =
=3D misc.getmetrics().gc_steps_atomic<br class=3D"">+while =
(misc.getmetrics().gc_steps_atomic =3D=3D old_steps_atomic) do<br =
class=3D"">+ collectgarbage('step')<br class=3D"">+ usets() =
-- luacheck: no global<br class=3D"">+end<br class=3D"">+<br =
class=3D"">+test:ok(true)<br class=3D"">+os.exit(test:check() and 0 or =
1)<br class=3D"">--<span class=3D"Apple-converted-space"> </span><br =
class=3D"">2.31.0<br class=3D""><br class=3D""></blockquote><br =
class=3D"">[1]: <a =
href=3D"https://lists.tarantool.org/tarantool-patches/20210719073632.12008=
-1-skaplun@tarantool.org/T/#u" =
class=3D"">https://lists.tarantool.org/tarantool-patches/20210719073632.12=
008-1-skaplun@tarantool.org/T/#u</a><br class=3D""><br class=3D"">--<span =
class=3D"Apple-converted-space"> </span><br class=3D"">Best =
regards,<br class=3D"">IM<br class=3D""></blockquote><br =
class=3D"">--<span class=3D"Apple-converted-space"> </span><br =
class=3D"">Best regards,<br class=3D"">Sergey Kaplun<br =
class=3D""></blockquote><br class=3D"">--<span =
class=3D"Apple-converted-space"> </span><br class=3D"">Best =
regards,<br class=3D"">IM<br class=3D""></blockquote><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">--<span =
class=3D"Apple-converted-space"> </span></span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; =
font-size: 11px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">Best =
regards,</span><br style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none;" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); font-family: =
Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; float: none; display: inline !important;" class=3D"">Sergey =
Kaplun</span></div></blockquote></div><br class=3D""></div></body></html>=
--Apple-Mail=_280D9147-E72B-4DC1-9FE3-5CD77A99F455--