Re: [PATCH 2/2] remoteproc: Remove firmware_loading_complete

[Sarangdhar Joshi]

On 12/16/2016 11:28 AM, Bjorn Andersson wrote:
> On Fri 16 Dec 00:26 PST 2016, loic pallardy wrote:
>
> > On 12/16/2016 01:03 AM, Sarangdhar Joshi wrote:
> > > rproc_del() waits on firmware_loading_complete in order to
> > > make sure rproc_add() completed successfully before calling
> > > rproc_shutdown().  However since rproc_add() will always be
> > > called before rproc_del(), we do not need to wait on
> > > firmware_loading_complete. Drop this completion variable
> > > altogether.
> > Hi,
> >
> > firmware_loading_complete is used to synchronize all operations on rproc
> > with parallel work launched by request_firmware_nowait.
>
> We had a deadlock scenario in this code, where a call to rproc_boot()
> would grab the rproc mutex and the request_firmware_nowait() callback
> would wait on this lock before it would signal the completion that the
> rproc_boot() was waiting for.
>
> As the request_firmware_nowait() doesn't do anything other than handle
> auto_boot and signal the completion - and there is an internal sleep
> mechanism for handling concurrent request_firmware calls - I posted a
> patch and dropped the rproc_boot() wait thing.

That's right. Should have added reference to commit
"e9b4f9efff5021 ("remoteproc: Drop wait in __rproc_boot()")"

> > rproc_add could be done and firmware loading still pending. In that case
> > rproc_del mustn't be called before end of the procedure.
>
> You're right.
>
> We might have an outstanding request_firmware_nowait() when we hit
> rproc_del() and we might free the underlaying rproc context.
>
> Holding a reference over the request_firmware_nowait() would solve this,
> but would cause issues if we get a rproc_add() from the same driver
> (e.g. after module unload/load) before the firmware timer has fired -
> and released the resources.

The asynchronous work request_firmware_work_func() is protected by 
get_device()/put_device() on remoteproc device. So we are probably 
covered for remoteproc device. However, I agree that parent device will 
still be an issue.

> This issue could be remedied by moving the rproc_delete_debug_dir() to
> rproc_del() and aim for not having any objects exposed outside the
> remoteproc core once rproc_del() returns.
>
> > If you decide to remove this synchronization you need either to modify rproc
> > boot sequence or to replace it by something else.
>
> I agree.

I agree too. rproc_boot() calls for non auto_boot case anyway calls 
request_firmware(). So calling __request_firmware asynchronously for non 
auto_boot case seems redundant. I was planning to send a patch to  call 
rproc_add_virtio_devices() for auto_boot case only. I guess I'll need to 
take care of only auto_boot case for the current issue then.

Regards,
Sarang

> Regards,
> Bjorn


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