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

Jingyi Wang
2026-04-16T02:52:24Z

On 4/14/2026 4:27 PM, Stephan Gerhold wrote:
> On Tue, Apr 14, 2026 at 11:23:50AM +0800, Jingyi Wang wrote:
>> On 4/10/2026 10:15 PM, Stephan Gerhold wrote:
>>> 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.
>>>
>>> @@ -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;
>>
>> In this case, rproc_crash_handler_work()->rproc_trigger_recovery()->
>> rproc_boot_recovery()->rproc_stop()->glink_subdev_stop() is called,
>> "rproc->state = RPROC_CRASHED" is set in the rproc_crash_handler_work
>> before rproc_boot_recovery is called, so checking RPROC_DETACHED can
>> not work for this case.
>>
>
> You're right, I forgot about that. I think we need a more generic
> solution for this though. rproc_stop_subdevices() should not be called
> without a prior call to rproc_start_subdevices().
>
> I think there are a couple of options for this:
>
> - Add a bool "subdevs_started" to struct rproc and manage that
> separately from the rproc->state.
>
> - Track the rproc state before the crash separately (something like
> rproc->state_before_crash) and check that in the stop path.
>
> - Add a new state RPROC_CRASHED_DETACHED to make sure the states are
> unique.
>
> - ...
>

Sure, I think a bool like subdevs_started will be better for maintain?

> Does the same issue also exist in qcom_pas_stop() of "[PATCH v5 4/5]
> remoteproc: qcom: pas: Add late attach support for subsystems" [1]?
> There you check for pas->rproc->state != RPROC_ATTACHED, wouldn't this
> also fail for the RPROC_CRASHED case?
>

I tested calling rproc_report_crash directly during qcom_pas_attach but
did not see issue, handover_issued is set only if attach is success
so "handover = qcom_q6v5_unprepare(&pas->q6v5);" will return false and
"qcom_pas_handover(&pas->q6v5);" will not be called.

Thanks,
Jingyi

> Thanks,
> Stephan
>
> [1]: https://lore.kernel.org/linux-arm-msm/20260409-knp-soccp-v5-4-805a492124da@oss.qualcomm.com/