crash deleting EffectState after starting up with an effect unit assigned to multiple input channels

[Stefan]

I build current master on github (last commit https://github.com/mixxxdj/mixxx/commit/310e459b1979cab5950bc76140e9b71adab223ce)

started Mixxx, selected Skin Shade and enabled the Effects via "FX" Button.

If I now switch the selected effect on effectunit 2 (the right side) Effect 1 by pressing one of the arrows of Effect 1, followed by pressing any of the arrows of Effect 1/2 in effectunit 1 or 2 mixxx crash with a "segmentation fault".

In fact after you pressed one's one of the two arrows of Effect 1 of effectunit 2 all buttons/sliders of all effects units will crash mixxx..

back-trace:
https://www.pastebin.ca/3952987

This only appears with Skin Shade, as the other Skins have different approaches to change the effects.

With mixxx 2.0 this doesn't happens.

running on Linux x64
Kernel 4.10.0-42-generic #46~16.04.1-Ubuntu
gcc v5.4.0 20160609
scons v2.4.1

[Stefan (nopeppermint)]

just compiled branch 2.1, it also happens with last commit (https://github.com/mixxxdj/mixxx/commit/adf8d4bfe1e2a1bd6af69524cb04da1c78ddb598)

In the new back-trace you find as well some "SKIN ERROR" they were here also before, but I didn't copied them to pastebin.

https://pastebin.ca/3953020

[Be (be.ing)]

Can you attach ~/.mixxx/effects.xml?

[Be (be.ing)]

This seems to happen whenever either the graphic or parametric EQ effects are loaded from effects.xml. I don't know why it doesn't happen when those effects are not loaded on startup...

[Be (be.ing)]

Ah, actually the problem seems to be when starting up with an effect unit assigned to one of the crossfader buses..

[Be (be.ing)]

I think I have identified exactly the conditions to reproduce this. On startup, an effect unit must:
1. Load an effect from effects.xml
2. Be routed to any deck
3. Be routed to any non-deck input. This could be a special bus like a crossfader bus or a non-deck EngineChannel like an auxiliary or mic input.

[Stefan (nopeppermint)]

>> attach ~/.mixxx/effects.xml

https://www.sendspace.com/file/67mtxp

[Stefan (nopeppermint)]

I now deleted my directory ~/.mixxx/effects.xml
and now I do no longer have this crash...

[Stefan (nopeppermint)]

to be precise i deleted the whole ~/.mixxx directory

[Stefan (nopeppermint)]

now after some effects loaded again a crash

https://pastebin.ca/3953080

https://www.sendspace.com/file/4itulx

attached the selected Effects (in all 4 Effect units) in Tango, after this is switched to Shade (which only has two effect units)

a second time the crash Error message was different:

https://pastebin.ca/3953082

let me know if you need something else

[Stefan (nopeppermint)]

and here the tango screenshot

[Be (be.ing)]

Did you try to enable effects within Shade since deleting all of ~/.mixxx? Note that the state of the routing switches is stored in ~/.mixxx/mixxx.cfg, not ~/.mixxx/effects.xml.

[Be (be.ing)]

Currently Shade only shows the routing switches for the left and right crossfader buses but no other skins show those yet. On startup, if there are no states set for the deck assignment switches, unit 1 will be assigned to deck 1, unit 2 to deck 2, and so on, but the deck assignment switches are not implemented in Shade.

[Stefan (nopeppermint)]

<Did you try to enable effects within Shade since deleting all of ~/.mixxx? Note that the state of the routing switches is stored in ~/.mixxx/mixxx.cfg, not ~/.mixxx/effects.xml.

My steps:
1. delete ~.mixxx completely with "rm -rf ~.mixxx/
2. gdb ./mixxx
3. (gdb) set height 0
4. (gdb) run
5. mixxx dialog to select library directory
6. mixxx starts with skin latenight
7. switch to skin shade
8. select some effects
9. switch to skin Tango, enable fx 3/4
10 switch back to Shade, change effects
everything ok till here, so I decided to do a restart of mixxx, and then after two button pressed, a crash happend again.

https://www.pastebin.ca/3953307

I see some interesting lines in the log:

during the shutdown of mixxx, I pressed the exit Button on the top right (before the crash):
<Warning [LibraryScanner 1]: QSqlDatabasePrivate::removeDatabase: connection 'MIXXX-2' is still in use, all queries will cease to work.

but then:
<[Inferior 1 (process 4671) exited normally]

Then during startup (after which I can crash mixxx with two effect changes):

<(gdb) run
<Starting program: /home/stefan/mixxx_master/mixxx/mixxx
<Warning [Main]: Configuration file is at version "2.0.0-release" instead of the <current 2.1.0-beta1

[Be (be.ing)]

I figured out what is causing this. EffectChain::enableForInputChannel keeps reusing the same array for EffectStates and putting a pointer to this on the effects MessagePipe. This assumes that the engine has a chance to process the message to load the states by calling EffectProcessorImpl::loadStatesForInputChannel before the next call to EffectChain::enableForInputChannel. On startup, before the engine starts, this assumption is not true. The result is that EffectProcessorImpl ends up storing pointers to the same EffectStates for multiple input channels. This causes a crash when ~EffectProcessorImpl tries to delete the EffectStates for the second input channel because the EffectState has already been deleted when deleting the EffectStates for the first input channel. The solution is to decouple the array of EffectStates for the MessagePipe from the EffectChain and send a new array for each ENABLE_EFFECT_CHAIN_FOR_INPUT_CHANNEL message.

[Be (be.ing)]

The commit that caused this was https://github.com/mixxxdj/mixxx/pull/1254/commits/3ea97980f6e56e53306b2335d2501647bd112f7d

[Be (be.ing)]

https://github.com/mixxxdj/mixxx/pull/1469

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/9033