From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from [87.239.111.99] (localhost [127.0.0.1]) by dev.tarantool.org (Postfix) with ESMTP id 6717C6EC40; Mon, 9 Aug 2021 19:03:13 +0300 (MSK) DKIM-Filter: OpenDKIM Filter v2.11.0 dev.tarantool.org 6717C6EC40 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=tarantool.org; s=dev; t=1628524993; bh=M4AjFRoGqv2aT4pwfguNYZ4StO1/4ctNpRF01UiO+uQ=; h=Date:To:References:In-Reply-To:Subject:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=FA1LJ1OmPGh+F5WWKm/LLg/erL/wqpY0fTJhelXrB4HtMuQ4H/7ovR0Wcz2un04ni jgGNOYo7rSi9/SHZ5v4DSSQEyLwx/QzWGXDnJQqC/VFh7dRSGhVJPmCaiMxqdfY/U9 9son8z+/eIb2D1b6tnwiMEOq6+6gsjtw/T4L71oE= Received: from smtp3.mail.ru (smtp3.mail.ru [94.100.179.58]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id E1EB96EC40 for ; Mon, 9 Aug 2021 19:03:10 +0300 (MSK) DKIM-Filter: OpenDKIM Filter v2.11.0 dev.tarantool.org E1EB96EC40 Received: by smtp3.mail.ru with esmtpa (envelope-from ) id 1mD7k5-0001QI-N5; Mon, 09 Aug 2021 19:03:10 +0300 Date: Mon, 9 Aug 2021 19:01:54 +0300 To: Igor Munkin Message-ID: References: <20210707143606.3499-1-skaplun@tarantool.org> <20210801103955.GY27855@tarantool.org> <20210808192846.GH27855@tarantool.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210808192846.GH27855@tarantool.org> X-4EC0790: 10 X-7564579A: 646B95376F6C166E X-77F55803: 4F1203BC0FB41BD92087353F0EC44DD910164DC12A5633065676A9727AC27C74182A05F538085040653C9753C3406833557425F559B879738F487CEDFB01DBAEDC53FE08B54FD4BD X-7FA49CB5: FF5795518A3D127A4AD6D5ED66289B5278DA827A17800CE7D8156D3FCB551F18EA1F7E6F0F101C67BD4B6F7A4D31EC0BCC500DACC3FED6E28638F802B75D45FF8AA50765F79006378BCFB34D7DDF138E8638F802B75D45FF36EB9D2243A4F8B5A6FCA7DBDB1FC311F39EFFDF887939037866D6147AF826D83B5EB0DBEDDC04471D55CD8D2052529E117882F4460429724CE54428C33FAD305F5C1EE8F4F765FCAE9A1BBD95851C5BA471835C12D1D9774AD6D5ED66289B52BA9C0B312567BB23117882F446042972877693876707352026055571C92BF10FC26CFBAC0749D213D2E47CDBA5A96583BA9C0B312567BB231DD303D21008E29813377AFFFEAFD269A417C69337E82CC2E827F84554CEF50127C277FBC8AE2E8BA83251EDC214901ED5E8D9A59859A8B6A45692FFBBD75A6A089D37D7C0E48F6C5571747095F342E88FB05168BE4CE3AF X-C1DE0DAB: 0D63561A33F958A51D48667E08F505AADBEBE62963FEE69B7D27F2EE60D4FB1DD59269BC5F550898D99A6476B3ADF6B47008B74DF8BB9EF7333BD3B22AA88B938A852937E12ACA75258990C0CF215F13410CA545F18667F91A7EA1CDA0B5A7A0 X-C8649E89: 4E36BF7865823D7055A7F0CF078B5EC49A30900B95165D343D50AEDB859DBAD9B70A6C8D1D02830454BB6ECB107E0BEDF742169BF62D864F412A1705237543401D7E09C32AA3244C98412A6D1B5C447ADAE0115AE80B7AA405AB220A9D022EBCFACE5A9C96DEB163 X-D57D3AED: 3ZO7eAau8CL7WIMRKs4sN3D3tLDjz0dLbV79QFUyzQ2Ujvy7cMT6pYYqY16iZVKkSc3dCLJ7zSJH7+u4VD18S7Vl4ZUrpaVfd2+vE6kuoey4m4VkSEu530nj6fImhcD4MUrOEAnl0W826KZ9Q+tr5ycPtXkTV4k65bRjmOUUP8cvGozZ33TWg5HZplvhhXbhDGzqmQDTd6OAevLeAnq3Ra9uf7zvY2zzsIhlcp/Y7m53TZgf2aB4JOg4gkr2biojGhQhWEp1aB9joptxVvqORQ== X-Mailru-Sender: 3B9A0136629DC91206CBC582EFEF4CB432F508E9BDB436F9611D3954042E4F6D463FF4E5A6303E51F2400F607609286E924004A7DEC283833C7120B22964430C52B393F8C72A41A89437F6177E88F7363CDA0F3B3F5B9367 X-Mras: Ok Subject: Re: [Tarantool-patches] [PATCH luajit] ARM64: Fix write barrier in BC_USETS. X-BeenThere: tarantool-patches@dev.tarantool.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Sergey Kaplun via Tarantool-patches Reply-To: Sergey Kaplun Cc: tarantool-patches@dev.tarantool.org Errors-To: tarantool-patches-bounces@dev.tarantool.org Sender: "Tarantool-patches" Igor, thanks for the feedback! On 08.08.21, Igor Munkin wrote: > Sergey, > > Thanks for the fixes! See some new comments below. > > On 01.08.21, Sergey Kaplun wrote: > > Igor, > > > > Thanks for the review! > > Update commit message on the branch, considering you comments. > > Got it, but I still have some more comments regarding it. > > > > > See answers to you questions below. > > > > > > > > > > > > > > | 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. > > > > > > OK, I understand almost nothing from the part above. Here are the > > > comments: > > > 1. "If it equals NULL (the first `#0`)", then what? > > > > My bad: > > I mean here: > > If it equals NULL (the first `#0`), then the upvalue is open. > > So why do you use NULL instead of 0? The field is uint8_t type, so 0 is > much clearer. Changed. > > > Added this. > > > > > 2. Just to check we are on the same page: the second "immediate" > > > mentioned in docs[1] is NZCV? > > > > Yes. > > > > > Then beq <1 branch is not taken since > > > (TMP0w != 0) is FALSE (i.e. upvalue is not closed), but zero flag in > > > NZCV value is not set? > > > > Yes. > > > > > So how does the color of the value to be stored > > > relate to this control flow? > > > > This NZCV value isn't set if the upvalue is white, because condition is > > of the following instruction > > > > | tst TMP1w, #LJ_GC_WHITES // iswhite(str) > > > > is TRUE. So the <1 branch is taken, because the upvalue is closed. > > 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). > > > > > > 3. AFAICS, if the branch is not taken and is called at > > > propagate or atomic phase, the value is colored either to gray or black. > > > > Yes, that leads to the assertion failure mentioned in the ticket in the > > LuaJIT upstream. > > > > > > > > > > > > > This patch changes yielded NZCV condition flag to 4 (Zero flag is up) to > > > > take the correct branch after `ccmp` instruction. > > > > > > > > Sergey Kaplun: > > > > * added the description and the test for the problem > > > > > > > > [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 > > > > > > Minor: Why #5629 is not mentioned? > > > > Added. > > 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 Updated, as you've suggested. > > > > > > > > > > > > > > > > > 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 > > > > > > > > > > > > > > > > > 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 = require('tap') > > > > + > > > > +local test = 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 > > > > > > Minor: I'm not sure, we need a separate lexical block here. Could you > > > please clarify the reason in the comment? > > > > 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. > > My bad. Yes, the easiest way to emit UCLO bytecode is using a separate > lexical block. > > > > > > > > > > + 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. > > > > > > Then what does it test, if the constant is marked as gray? Will this > > > string be white later? > > > > It shouldn't be white, it should be gray, otherwise the aforementioned > > condition is TRUE (remember, we need FALSE). > > Again, PEBKAC, thanks for the explanation. > > > > > > > > > > + local function usets() uv = '' end > > > > + _G.usets = usets > > > > +end > > > > + > > > > +-- Set GC state to GCpause. > > > > +collectgarbage() > > > > +-- Do GC step as often as possible. > > > > +collectgarbage('setstepmul', 100) > > > > > > Minor: Don't get, why you need to make GC less aggressive for the test. > > > The test is run, until propagate phase is finished. > > > > 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. > > Drop it, please. I can't even *feel* its effect ;) Done. > > > > > > > > > > + > > > > +-- 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. > > Minor: It would be nice to drop a few words about string and upvalue > colours during this loop, but it's up to you. Added. The iterative patch is the following: =================================================================== 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 -- Set GC state to GCpause. collectgarbage() --- Do GC step as often as possible. -collectgarbage('setstepmul', 100) +-- 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. =================================================================== > > > > > +local old_steps_atomic = misc.getmetrics().gc_steps_atomic > > > > +while (misc.getmetrics().gc_steps_atomic == old_steps_atomic) do > > > > + collectgarbage('step') > > > > + usets() -- luacheck: no global > > > > +end > > > > + > > > > +test:ok(true) > > > > +os.exit(test:check() and 0 or 1) > > > > -- > > > > 2.31.0 > > > > > > > > > > [1]: https://lists.tarantool.org/tarantool-patches/20210719073632.12008-1-skaplun@tarantool.org/T/#u > > > > > > -- > > > Best regards, > > > IM > > > > -- > > Best regards, > > Sergey Kaplun > > -- > Best regards, > IM -- Best regards, Sergey Kaplun