ipc: run buffer free in context of active pipeline

[kv2019i]

BUFFER_FREE IPC returns an error if buffer is connected to
two active components.

However it is allowed to free a buffer in the case where either the sink
or the source is no longer active. This happens for example with buffers
that connect two pipelines. If one pipeline is stopped and freed,
the connecting buffer will be also freed.

This does mean pipeline_disconnect() may be run in context
of a pipeline that is running on a different core. This is
fundamentally unsafe and can lead to undefined behaviour
when two cores access the pipeline bsource_list/bsink_list
at the same time on two different cores.

Fix this issue by checking for this case, and running
the BUFFER_FREE on the active core.

The change is not sufficient on its own, but is part of the fixes
to address: #5469

Signed-off-by: Kai Vehmanen kai.vehmanen@linux.intel.com

[lgirdwood]

Fwiw, @RanderWang doing a similar fix for IPC4

[lyakh]

this is hitting the "buffer core" topic again. This has been discussed before and my understanding was, that we were trying to achieve the following status:

1. any connected pipelines should run on the same core. Different cores aren't currently supported and would also be difficult to support without major changes to the code base
2. (1) also implies that all components within a single pipeline should run on the same core
3. buffer->core is then redundant, since all buffers have source and sink components handled by the same core, so buffers are never shared.

If the above is correct, can we make it explicit? If it isn't, we need test-cases...

[lgirdwood]

1. any connected pipelines should run on the same core. Different cores aren't currently supported and would also be difficult to support without major changes to the code base

Different cores should be supported for connected pipelines especially with Zephyr.