Re: [PATCH 0/7] slimbus: qcom-ngd-ctrl: Fix some race conditions and deadlocks

[Bjorn Andersson <andersson@kernel.org>]

On Wed, Mar 11, 2026 at 03:40:46AM +0200, Dmitry Baryshkov wrote:
> On Mon, Mar 09, 2026 at 11:09:01PM -0500, Bjorn Andersson wrote:
> > When the qcom-ngd-ctrl driver is probed after the ADSP remoteproc, the
> > SSR notifier will fire immediately, which results in
> > qcom_slim_ngd_ssr_pdr_notify() attempting to schedule_work() on an
> > unitialized work_struct.
> > 
> > The concrete result of this is that my db845c/RB3 now fails to boot 100%
> > of the time.
> > 
> > In reviewing the problematic code, a few other problems where
> > discovered, such that platform_driver_unregister() is used to unregister
> > the child device.
> > 
> > Lastly, with the db845c booting, it was determined that attempting to
> > stop the ADSP remoteproc causes the slimbus driver to deadlock.
> > 
> > Note that while this solves the problems described above, and unblock
> > boot as well as restart of the remoteproc, this stack needs more love.
> > 
> > Upon tearing down the slimbus controller (when the ADSP goes down), the
> > slimbus devices attempts to access their slimbus devices - which is
> > prevented by the controller being runtime suspended. This results in a
> > wall of errors in the log, about failing transactions.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
> > ---
> > Bjorn Andersson (7):
> >       slimbus: qcom-ngd-ctrl: Fix up platform_driver registration
> >       slimbus: qcom-ngd-ctrl: Fix probe error path ordering
> >       slimbus: qcom-ngd-ctrl: Correct PDR and SSR cleanup ownership
> >       slimbus: qcom-ngd-ctrl: Register callbacks after creating the ngd
> >       slimbus: qcom-ngd-ctrl: Initialize controller resources in controller
> >       slimbus: qcom-ngd-ctrl: Balance pm_runtime enablement for NGD
> >       slimbus: qcom-ngd-ctrl: Avoid ABBA on tx_lock/ctrl->lock
> > 
> >  drivers/slimbus/qcom-ngd-ctrl.c | 127 +++++++++++++++++++++++++---------------
> >  1 file changed, 80 insertions(+), 47 deletions(-)
> > ---
> > base-commit: a0ae2a256046c0c5d3778d1a194ff2e171f16e5f
> > change-id: 20260211-slim-ngd-dev-74166f29f035
> > 
> > Best regards,
> > -- 
> > Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
> 
> Bjorn,
> 
> While you are at it, it looks like there is another possible issue:
> ngd->base is set after platform_device_add(), possibly letting NGD
> driver to use uninitialized base.
> 

ngd->base is only dereferences from qcom_slim_ngd_up_worker() and
qcom_slim_ngd_runtime_resume(), so at this time there's no concrete
problem here.

I'll keep it in mind as I continue to poke at the driver.

Regards,
Bjorn

> -- 
> With best wishes
> Dmitry