Bug 33277 - test-privserver always crashes and nobody noticed
Summary: test-privserver always crashes and nobody noticed
Status: RESOLVED FIXED
Alias: None
Product: dbus
Classification: Unclassified
Component: core (show other bugs)
Version: 1.4.x
Hardware: Other All
: high major
Assignee: Simon McVittie
QA Contact: John (J5) Palmieri
URL: http://git.collabora.co.uk/?p=user/sm...
Whiteboard: 1.4
Keywords: patch
Depends on:
Blocks:
 
Reported: 2011-01-19 09:28 UTC by Simon McVittie
Modified: 2011-02-02 07:19 UTC (History)
1 user (show)

See Also:
i915 platform:
i915 features:


Attachments
[1/3] test_server_setup: on OOM while setting up watch/timeout, don't leak sd (1.04 KB, patch)
2011-01-19 09:42 UTC, Simon McVittie
Details | Splinter Review
[2/3] test_server_setup: allocate two server-data blobs, for watches and timeouts (1.30 KB, patch)
2011-01-19 09:43 UTC, Simon McVittie
Details | Splinter Review
[3/3] test_server_shutdown: disconnect the server before causing it to be freed (903 bytes, patch)
2011-01-19 09:44 UTC, Simon McVittie
Details | Splinter Review
test-privserver-client: wait for server to die between iterations (6.15 KB, patch)
2011-01-20 05:46 UTC, Simon McVittie
Details | Splinter Review
[alternative patch 2] test_server_setup: allocate two server-data blobs, for watches and timeouts (2.81 KB, patch)
2011-01-21 06:25 UTC, Simon McVittie
Details | Splinter Review

Description Simon McVittie 2011-01-19 09:28:20 UTC
test-privserver always crashes with an assertion failure, because nobody called dbus_server_disconnect(). As far as I can see from the git history, it's always done this...

There are several things wrong here:

* On one of my branches, the tests fail as a result (I'm not sure why,
  but I'm refactoring the main loop, so it might be timing-related).

* Tests seem as though they ought to be fairly exemplary; this one clearly
  isn't!

* Our test framework doesn't normally notice that part of the test has
  crashed. This is lower-priority, but concerning.

Patches on the way.
Comment 1 Simon McVittie 2011-01-19 09:42:50 UTC
Created attachment 42204 [details] [review]
[1/3] test_server_setup: on OOM while setting up watch/timeout, don't leak sd

A related fix for part of Bug #33128 (see attachment 42058 [details] [review] for an earlier version, rejected in the 18th comment on Bug #33128).
Comment 2 Simon McVittie 2011-01-19 09:43:47 UTC
Created attachment 42205 [details] [review]
[2/3] test_server_setup: allocate two server-data blobs, for watches and timeouts

This is similar to how ConnectionData works. Without this change, we
deserve to segfault: when the first set of callbacks (either watches or
timeouts) is cleaned up, we unref the server and loop, and free sd;
when the second set of callbacks is cleaned up, we use-after-free sd,
the server and the loop, then double-free sd.

However, due to fd.o #33277 we don't even get that far, because we've
already died with an assertion failure.
Comment 3 Simon McVittie 2011-01-19 09:44:32 UTC
Created attachment 42206 [details] [review]
[3/3] test_server_shutdown: disconnect the server before causing it to be freed

Otherwise we die with an assertion failure.

(This is the actual fix for this bug.)
Comment 4 Simon McVittie 2011-01-19 09:55:13 UTC
Those patches don't address the failure to detect failure, but they're enough to drop the severity of this bug once applied.

To test manually:

./test/name-test/test-privserver (in one window)

./test/name-test/test-privserver-client (in another window)

The client test will fail, because test-privserver exits after one request, test-privserver-client wants to make four requests, and test-privserver probably isn't activatable on your normal session bus. However, at least neither actually crashes now.

The error I'm seeing on a work-in-progress branch seems to be unrelated, though; I might have broken dbus-daemon on that branch or something.
Comment 5 Simon McVittie 2011-01-20 05:46:32 UTC
Created attachment 42225 [details] [review]
test-privserver-client: wait for server to die between iterations

This fixes a race condition: the server exits while the client continues
to the next iteration. If the server wins, the test passes. If the client
wins, it sends a message to the dying service, never gets a reply, and the
test fails.

My branch to refactor the main loop for fd.o #23194 seems to make the
client more likely to win this race, resulting in intermittent test
failures.

This is an instance of the general problem described by Bug #11454.

> The error I'm seeing on a work-in-progress branch seems to be unrelated,
> though

It turned out to be this vaguely related race condition.
Comment 6 Colin Walters 2011-01-20 14:20:57 UTC
Comment on attachment 42204 [details] [review]
[1/3] test_server_setup: on OOM while setting up watch/timeout, don't leak sd

>From dae7a0c5eba6d05a2c595c86bcf85cc7839f9b40 Mon Sep 17 00:00:00 2001
>From: Simon McVittie <simon.mcvittie@collabora.co.uk>
>Date: Wed, 19 Jan 2011 17:28:58 +0000
>Subject: [PATCH 1/3] test_server_setup: on OOM while setting up watch/timeout, don't leak sd

Looks good.
Comment 7 Colin Walters 2011-01-20 14:22:52 UTC
Comment on attachment 42205 [details] [review]
[2/3] test_server_setup: allocate two server-data blobs, for watches and timeouts

>From 26d5655dfbc562cc7721826b5d7f4b4a553f356f Mon Sep 17 00:00:00 2001
>From: Simon McVittie <simon.mcvittie@collabora.co.uk>
>Date: Wed, 19 Jan 2011 17:33:31 +0000
>Subject: [PATCH 2/3] test_server_setup: allocate two server-data blobs, for watches and timeouts

This is pretty ugly; how hard is it to refcount serverdata instead?
Comment 8 Colin Walters 2011-01-20 14:23:54 UTC
Comment on attachment 42206 [details] [review]
[3/3] test_server_shutdown: disconnect the server before causing it to be freed

>From ebf31ed7fec8a5a10c621e2a051f918a03d3ed6b Mon Sep 17 00:00:00 2001
>From: Simon McVittie <simon.mcvittie@collabora.co.uk>
>Date: Wed, 19 Jan 2011 17:34:10 +0000
>Subject: [PATCH 3/3] test_server_shutdown: disconnect the server before causing it to be freed

Looks fine.
Comment 9 Simon McVittie 2011-01-21 06:25:23 UTC
Created attachment 42269 [details] [review]
[alternative patch 2] test_server_setup: allocate two server-data blobs, for watches and timeouts

(In reply to comment #6)
> >Subject: [PATCH 1/3] test_server_setup: on OOM while setting up watch/timeout, don't leak sd
> 
> Looks good.

Thanks, applied.

(In reply to comment #7)
> >Subject: [PATCH 2/3] test_server_setup: allocate two server-data blobs, for watches and timeouts
> 
> This is pretty ugly; how hard is it to refcount serverdata instead?

I started writing that first, in fact; it's easy, but seemed an unreasonable amount of boilerplate for a 2-word blob containing two refcounted objects, particularly for test code, so I threw it away.

4 insertions seem better for my insertion/deletion karma than 23 insertions/6 deletions, but if you'd strongly prefer the refcounted version, here it is (the branch is serverdata-33128-alt in my git repository).

I haven't applied Attachment #42206 [details] yet despite your positive review, since it isn't enough to make the test not crash (either Attachment #42205 [details] or this one is necessary first).

For reliable tests, Attachment #42225 [details] would also be good to have.
Comment 10 Simon McVittie 2011-01-24 08:22:29 UTC
I think this is unintrusive enough for 1.4.
Comment 11 Will Thompson 2011-02-02 06:53:37 UTC
Review of attachment 42225 [details] [review]:

Looks good.
Comment 12 Simon McVittie 2011-02-02 07:19:50 UTC
Reviewed by wjt on IRC and fixed in git for 1.4.4, 1.5.0. Thanks!


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