Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> Gilles Chanteperdrix wrote: >>> However, I do not have a strong opinion on this, it is just an open >>> question. More generally, I would like us to discuss once and for all >>> about the semantic of the various calls and their effect on the RT_TASK >>> duration, instead of changing this semantic every release and risk >>> breaking non-broken applications (I mean, the one which do not segfault). >> To pick up this issue again (in order to get my queue flushed): >> >> We basically have to decide about the question what rt_task_delete >> invalidates and what impact this shall have on rt_task_join. It is >> already documented that rt_task_delete invalidates (and releases) the >> kernel-side resources of a RT_TASK. The question is what shall happen to >> the not explicitly mentioned user-side resources (ie. the pthread - >> where available). >> >> Option 1 is to decouple both and keep the user side of a joinable >> RT_TASK alive until it is explicitly joined. Option 2 could be to >> declare both parts invalid on rt_task_delete. Based on this decision, >> the finalization logic of rt_task_delete and rt_task_join then needs to >> be adjusted to deliver the right behavior, including proper error codes >> instead of sporadic SEGV. > > Relying on the contents of the RT_TASK structure to know the state of a > task is bound to fail: the RT_TASK structure may be copied around, so > changing the contents of the RT_TASK structure in rt_task_delete, to use > that information later will only work if the same RT_TASK structure is > used later. This is fragile.
That's true but somehow the best we can do to detect errors that remain fuzzy otherwise. We neither have a list of all user space RT_TASK structs nor any in-kernel object to ask after rt_task_delete or join. > >> Do we expect applications to rely on this joinability after >> rt_task_delete? If yes, we should make it official, document the >> descriptor split and the fact that the descriptor cannot be looked up >> anymore after deletion but has to be saved beforehand. >> >> Independently, we need to clarify that cross-process join is not >> supported. Trying to do this ATM will result in a SEGV (something I >> missed so far). > > This is a regression. At some point in the past, a NULL pthread_t opaque > pointer was used to mean that the thread was living in a different > process, and rt_task_delete would skip the pthread_cancel. > I was talking about rt_task_join on a foreign RT_TASK. And I was wrong, it actually works with and without my patch SEGV-free. It just lacks documentation. But you did not address the core questions. Jan
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