[Kde-pim] resource crashes using deleted attribute

[Daniel Vrátil]

On Sunday, April 12, 2015 01:27:42 AM David Faure wrote:
> http://www.davidfaure.fr/2015/attribute-crash is a valgrind log of a crash
> in my akonadi resource.
> 
> Could there be a bug in the refcounting of Entity / Collection / Attribute?
> Somehow the ItemCreateJob destructor (indirectly) deletes the attribute in a
> collection that a CollectionModifyJob (which is still running) is using.
> 
> How could this happen?

Hi,

my only guess is that the problem could be in Entity copy ctor, which is 
employing some kind of hack to copy the shared Private data, but I don't 
really understand it much.

Dan

> 
> 
> My code is pretty standard I think:
> 
>      // Store timestamp into DB, to persist it across restarts
>             EntityAnnotationsAttribute *annotationsAttribute =
>                     mCollection.attribute<EntityAnnotationsAttribute>(
> Akonadi::Collection::AddIfMissing ); Q_ASSERT(annotationsAttribute);
>             if (annotationsAttribute->value(s_timeStampKey) !=
> mHandler->latestTimestamp()) { annotationsAttribute->insert(s_timeStampKey,
> mHandler->latestTimestamp());
> mCollection.addAttribute(annotationsAttribute);
> 
>                 // no parent, this job will outlive the ListEntriesJob
>                 Akonadi::CollectionModifyJob *modJob = new
> Akonadi::CollectionModifyJob(mCollection); Q_UNUSED(modJob);
>             }
>             q->emitResult();
> 
> (where mCollection is an Akonadi::Collection member in a class that will be
> deleted before that job is done -- but surely that's fine, given that
> Collection is a refcounted value class??)
> 
> EntityAnnotationsAttribute (from kdepimlibs/akonadi) isn't actually used
> anywhere (strangely enough), but its code is 100% like
> kdepim-runtime/resources/shared/collectionannotationsattribute.cpp so the
> problem isn't there.
> 
> If nobody knows I guess I'll have to debug that refcounting code.... the
> crash is reproduceable.

-- 
Daniel Vrátil
www.dvratil.cz | dvratil at kde.org
IRC: dvratil on Freenode (#kde, #kontact, #akonadi, #fedora-kde)

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