node_contextify: do not incept debug context #4819

MylesBorins · 2016-01-22T19:20:52Z

Currently a debug context is created for various calls to util.

If the node debugger is being run the main context is the debug
context. In this case node_contextify was freeing the debug context
and causing everything to explode.

This change checks to see if there is currently a debug context
before setting up / tearing down a temporary context.

mscdex · 2016-01-22T19:23:26Z

Can you also add a test for this?

mscdex · 2016-01-22T19:29:49Z

src/node_contextify.cc

-    ScopedEnvironment env_scope(debug_context, env);
+    const int index = Environment::kContextEmbedderDataIndex;
+    if (!debug_context->GetAlignedPointerFromEmbedderData(index)) {
+      ScopedEnvironment env_scope(debug_context, env);


Are you sure this is right? env_scope's destructor will get called as soon as execution moves outside of the if statement. I'm not sure, but we may need to have an if-else and copy the code after the current if into both blocks (one with env_scope and one without)?

Thanks for the heads up. I have not used structs with this pattern before and was unaware of the semantics.

MylesBorins · 2016-01-22T19:46:04Z

@mscdex I've attempted a different approach, does this solve your original concerns?

bnoordhuis · 2016-01-22T19:57:57Z

src/node_contextify.cc

@@ -246,14 +246,22 @@ class ContextifyContext {
    // there is no way for the embedder to tell if the data index is
    // in use.
    struct ScopedEnvironment {
+      bool alreadyInDebugContext = false;


Style: C++ code uses snake_case for locals.

EDIT: And data members use snake_case and end in an underscore: bool already_in_debug_context_ = false; Also, it should go near the definition of context_.

I rebased in those style changes in case we decide to move forward with 803ca9667a8dc608c5271633e42e792dbba66fc0

MylesBorins · 2016-01-22T20:01:42Z

@bnoordhuis I've just pushed another option for handling this problem.

@ofrobots was saying that my second attempt would cause a FATAL ERROR if the index slot didn't exist

The current approach, originally done as a patch shared by ofrobots does away with that, but no longer cleans up the debugger context, which may be undesirable

bnoordhuis · 2016-01-22T20:04:25Z

test.js

@@ -0,0 +1,3 @@
+var util = require('util');


'use strict'

bah... didn't mean to check that in.

killed that file.

bnoordhuis · 2016-01-22T20:04:48Z

LGTM with a nit and assuming the CI likes it.

MylesBorins · 2016-01-22T20:07:23Z

@bnoordhuis can I get you to sign off one more time on the current head. Just want to ensure that is the one you were ok with

bnoordhuis · 2016-01-22T20:09:04Z

LGTM but is there a reason you're not deassigning the context slot afterwards?

MylesBorins · 2016-01-22T20:10:54Z

the deassignment was what was causing the original problem

MylesBorins@724fb28 offers an approach with deassignment but causes the debug errors mentioned above. TBQH I am a little out of my depth here, and not sure the best way to only deassign if there was not already a debugger context

bnoordhuis · 2016-01-22T20:14:00Z

What worries me a little is that you're essentially leaving a dangling pointer. If you have a simple regression test, I can take a look.

ofrobots · 2016-01-22T20:15:53Z

@bnoordhuis See: #4815. The original problem is that there is code in util.js (e.g. inspectPromise) that now keeps a keep a debug context around forever. Once that context has been created, subsequent calls to RunInDebugContext clear the environment from the debug context when they shoudn't.

I am worried about the dangling pointer, but I think Environment lives longer as the debug context so I am not sure it really is dangling?

bnoordhuis · 2016-01-22T21:03:38Z

Not now, no, but it's a future hazard. Change itself LGTM but a regression test would be good.

MylesBorins · 2016-01-22T21:07:28Z

@bnoordhuis are there similar regression tests I can look at to base it off of?

bnoordhuis · 2016-01-22T21:22:11Z

Maybe the test from 25776f3?

MylesBorins · 2016-01-22T22:27:07Z

So the edge case does not seem to show up if debugger is being run in interactive mode.

Not having a ton of luck here

jasnell · 2016-01-23T04:27:47Z

Yeah, this one is a hard one. The change LGTM but it leaves me a bit uneasy. Unfortunately I haven't had any luck coming up with an idea for a reliable regression test either.

MylesBorins · 2016-02-03T20:04:54Z

ping @bnoordhuis

Trott · 2016-02-05T03:55:42Z

test/parallel/test-debugger-util-regression.js

+proc.stderr.setEncoding('utf8');
+
+function fail() {
+  assert(false, 'the program should not hang');


Nit: common.fail()

Trott · 2016-02-05T04:01:51Z

Test LGTM. Would be great if @bnoordhuis or @indutny or someone else knowledgable about the C++ side of things could give an LGTM. (Ben gave one, but it was 13 days ago and I'm pretty sure the code has changed since then.)

indutny · 2016-02-05T21:04:01Z

LGTM if CI is happy.

bnoordhuis · 2016-02-05T22:04:46Z

test/parallel/test-debugger-util-regression.js

+// exploding but is still not an elegant solution. Likely a deeper bug
+// causing this problem.
+proc.stdin.on('error', (err) => {
+  console.error(new Error(err));


err is already an Error, isn't it?

bnoordhuis · 2016-02-05T22:07:12Z

LGTM with teeny tiny nits. Can I suggest you stress-test the test besides doing the regular CI?

MylesBorins · 2016-02-05T22:43:14Z

Stress Test: https://ci.nodejs.org/job/node-stress-single-test/415/

edit: stress test had over 1400 positives and 0 negatives so I stopped it.

@3y3

Currently a debug context is created for various calls to util. If the node debugger is being run the main context is the debug context. In this case node_contextify was freeing the debug context and causing everything to explode. This change moves around the logic and no longer frees the context. There is a concern about the dangling pointer The regression test was adapted from code submitted by @3y3 in nodejs#4815 Fixes: nodejs#4440 Fixes: nodejs#4815 Fixes: nodejs#4597 Fixes: nodejs#4952 PR-URL: nodejs#4815 Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Rich Trott <rtrott@gmail.com>

MylesBorins · 2016-02-05T23:41:25Z

landed in 4897f94

Notable changes: * buffer: make byteLength work with Buffer correctly (Jackson Tian) - nodejs#4738 * debugger: guard against call from non-node context (Ben Noordhuis) - nodejs#4328 * node_contextify: do not incept debug context (Myles Borins) - nodejs#4819 * deps: update to http-parser 2.5.2 (James Snell) - nodejs#5238

Notable changes: * buffer: make byteLength work with Buffer correctly (Jackson Tian) - #4738 * debugger: guard against call from non-node context (Ben Noordhuis) - #4328 * node_contextify: do not incept debug context (Myles Borins) - #4819 * deps: update to http-parser 2.5.2 (James Snell) - #5238 PR-URL: #5200 (comment)

mscdex reviewed Jan 22, 2016
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mscdex added debugger vm Issues and PRs related to the vm subsystem. labels Jan 22, 2016

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jasnell mentioned this pull request Jan 23, 2016

In "node debug" in a certain reproducible scenario, typing "c" twice causes node to completley hang #4651

Closed

MylesBorins mentioned this pull request Jan 25, 2016

Broken example for vm.runInDebugContext(code) #4862

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MylesBorins self-assigned this Jan 25, 2016

MylesBorins mentioned this pull request Jan 26, 2016

Debugger protocol hangs in some special situations #4597

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MylesBorins force-pushed the do-not-double-debug branch from c0efa65 to 86a94ac Compare January 27, 2016 01:04

MylesBorins assigned bnoordhuis and unassigned MylesBorins Feb 3, 2016

Trott reviewed Feb 5, 2016
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MylesBorins mentioned this pull request Feb 5, 2016

util.inspect({level: "info"}) exits the debug session #4440

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mikermcneil mentioned this pull request Feb 5, 2016

Sails 0.12.0-rc6 debug error : Segmentation fault balderdashy/sails#3538

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chrisradek mentioned this pull request Feb 5, 2016

Logger facility causes crash or stall with NodeJs 4.2.5+ aws/aws-sdk-js#897

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bnoordhuis reviewed Feb 5, 2016
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MylesBorins force-pushed the do-not-double-debug branch 2 times, most recently from 9b84a8c to 54b8693 Compare February 5, 2016 22:41

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MylesBorins force-pushed the do-not-double-debug branch from 86aa7db to 4897f94 Compare February 5, 2016 23:41

MylesBorins merged commit 4897f94 into nodejs:master Feb 5, 2016

MylesBorins deleted the do-not-double-debug branch February 8, 2016 18:46

gzzhanghao mentioned this pull request Feb 10, 2016

Complete application crash when console.log()ing an object node-inspector/node-inspector#823

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MylesBorins added lts-watch-v4.x and removed lts-watch-v4.x labels Feb 11, 2016

MylesBorins mentioned this pull request Apr 5, 2016

When debugging, any console logging that outputs an object is terminating the debugger. #6066

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node_contextify: do not incept debug context #4819

node_contextify: do not incept debug context #4819

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node_contextify: do not incept debug context #4819

node_contextify: do not incept debug context #4819

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