Re: [PATCH 2/2] remoteproc: qcom: Check glink->edge in glink_subdev_stop()

[Stephan Gerhold <stephan.gerhold@linaro.org>]

On Thu, Apr 09, 2026 at 01:46:22AM -0700, Jingyi Wang wrote:
> For rproc that doing attach, glink_subdev_start() is called only when
> attach successfully. If rproc_report_crash() is called in the attach
> function, rproc_boot_recovery()->rproc_stop()->glink_subdev_stop() could
> be called and cause NULL pointer dereference:
> 
>  Unable to handle kernel NULL pointer dereference at virtual address 0000000000000300
>  Mem abort info:
>  ...
>  pc : qcom_glink_smem_unregister+0x14/0x48 [qcom_glink_smem]
>  lr : glink_subdev_stop+0x1c/0x30 [qcom_common]
>  ...
>  Call trace:
>   qcom_glink_smem_unregister+0x14/0x48 [qcom_glink_smem] (P)
>   glink_subdev_stop+0x1c/0x30 [qcom_common]
>   rproc_stop+0x58/0x17c
>   rproc_trigger_recovery+0xb0/0x150
>   rproc_crash_handler_work+0xa4/0xc4
>   process_scheduled_works+0x18c/0x2d8
>   worker_thread+0x144/0x280
>   kthread+0x124/0x138
>   ret_from_fork+0x10/0x20
>  Code: a9be7bfd 910003fd a90153f3 aa0003f3 (b9430000)
>  ---[ end trace 0000000000000000 ]---
> 
> Add NULL pointer check in the glink_subdev_stop() to make sure
> qcom_glink_smem_unregister() will not be called if glink_subdev_start()
> is not called.
> 

You mention the actual root problem here: Why is glink_subdev_stop()
called if glink_subdev_start() wasn't called?

The call to rproc_start_subdevices() in __rproc_attach() makes sure that
all subdevices are in consistent state when exiting the function (either
prepared+started or stopped+unprepared). Only if all subdevices were
started successfully, the rproc->state is changed to RPROC_ATTACHED.

In your case, attaching the rproc failed so the rproc->state should be
still RPROC_DETACHED. All subdevices should be stopped+unprepared. We
shouldn't stop/unprepare any subdevices again in this state, they all
might crash like glink does here.

We know that subdevices are already stopped+unprepared in RPROC_DETACHED
state, so I think you just need to skip rproc_stop_subdevices() and
rproc_unprepare_subdevices() inside rproc_stop() in this case, see diff
below.

Thanks,
Stephan

@@ -1708,8 +1709,9 @@ static int rproc_stop(struct rproc *rproc, bool crashed)
 	if (!rproc->ops->stop)
 		return -EINVAL;
 
-	/* Stop any subdevices for the remote processor */
-	rproc_stop_subdevices(rproc, crashed);
+	/* Stop any subdevices for the remote processor if it was attached */
+	if (rproc->state != RPROC_DETACHED)
+		rproc_stop_subdevices(rproc, crashed);
 
 	/* the installed resource table is no longer accessible */
 	ret = rproc_reset_rsc_table_on_stop(rproc);
@@ -1726,7 +1728,8 @@ static int rproc_stop(struct rproc *rproc, bool crashed)
 		return ret;
 	}
 
-	rproc_unprepare_subdevices(rproc);
+	if (rproc->state != RPROC_DETACHED)
+		rproc_unprepare_subdevices(rproc);
 
 	rproc->state = RPROC_OFFLINE;