Re: [PATCH v7 12/12] rpmsg: Fix kfree() of static memory on setting driver_override

[Krzysztof Kozlowski]

On 29/04/2022 16:51, Marek Szyprowski wrote:
> On 29.04.2022 16:16, Krzysztof Kozlowski wrote:
>> On 29/04/2022 14:29, Marek Szyprowski wrote:
>>> On 19.04.2022 13:34, Krzysztof Kozlowski wrote:
>>>> The driver_override field from platform driver should not be initialized
>>>> from static memory (string literal) because the core later kfree() it,
>>>> for example when driver_override is set via sysfs.
>>>>
>>>> Use dedicated helper to set driver_override properly.
>>>>
>>>> Fixes: 950a7388f02b ("rpmsg: Turn name service into a stand alone driver")
>>>> Fixes: c0cdc19f84a4 ("rpmsg: Driver for user space endpoint interface")
>>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
>>>> Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
>>> This patch landed recently in linux-next as commit 42cd402b8fd4 ("rpmsg:
>>> Fix kfree() of static memory on setting driver_override"). In my tests I
>>> found that it triggers the following issue during boot of the
>>> DragonBoard410c SBC (arch/arm64/boot/dts/qcom/apq8016-sbc.dtb):
>>>
>>> ------------[ cut here ]------------
>>> DEBUG_LOCKS_WARN_ON(lock->magic != lock)
>>> WARNING: CPU: 1 PID: 8 at kernel/locking/mutex.c:582
>>> __mutex_lock+0x1ec/0x430
>>> Modules linked in:
>>> CPU: 1 PID: 8 Comm: kworker/u8:0 Not tainted 5.18.0-rc4-next-20220429 #11815
>>> Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
>>> Workqueue: events_unbound deferred_probe_work_func
>>> pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>>> pc : __mutex_lock+0x1ec/0x430
>>> lr : __mutex_lock+0x1ec/0x430
>>> ..
>>> Call trace:
>>>    __mutex_lock+0x1ec/0x430
>>>    mutex_lock_nested+0x38/0x64
>>>    driver_set_override+0x124/0x150
>>>    qcom_smd_register_edge+0x2a8/0x4ec
>>>    qcom_smd_probe+0x54/0x80
>>>    platform_probe+0x68/0xe0
>>>    really_probe.part.0+0x9c/0x29c
>>>    __driver_probe_device+0x98/0x144
>>>    driver_probe_device+0xac/0x14c
>>>    __device_attach_driver+0xb8/0x120
>>>    bus_for_each_drv+0x78/0xd0
>>>    __device_attach+0xd8/0x180
>>>    device_initial_probe+0x14/0x20
>>>    bus_probe_device+0x9c/0xa4
>>>    deferred_probe_work_func+0x88/0xc4
>>>    process_one_work+0x288/0x6bc
>>>    worker_thread+0x248/0x450
>>>    kthread+0x118/0x11c
>>>    ret_from_fork+0x10/0x20
>>> irq event stamp: 3599
>>> hardirqs last  enabled at (3599): [<ffff80000919053c>]
>>> _raw_spin_unlock_irqrestore+0x98/0x9c
>>> hardirqs last disabled at (3598): [<ffff800009190ba4>]
>>> _raw_spin_lock_irqsave+0xc0/0xcc
>>> softirqs last  enabled at (3554): [<ffff800008010470>] _stext+0x470/0x5e8
>>> softirqs last disabled at (3549): [<ffff8000080a4514>]
>>> __irq_exit_rcu+0x180/0x1ac
>>> ---[ end trace 0000000000000000 ]---
>>>
>>> I don't see any direct relation between the $subject and the above log,
>>> but reverting the $subject on top of linux next-20220429 hides/fixes it.
>>> Maybe there is a kind of memory trashing somewhere there and your change
>>> only revealed it?
>> Thanks for the report. I think the error path of my patch is wrong - I
>> should not kfree(rpdev->driver_override) from the rpmsg code. That's the
>> only thing I see now...
>>
>> Could you test following patch and tell if it helps?
>> https://pastebin.ubuntu.com/p/rp3q9Z5fXj/
> 
> This doesn't help, the issue is still reported.

I think I screwed this part of code. The new helper uses device_lock()
(the mutexes you see in backtrace) but in rpmsg it is called before
device_register() which initializes the device.

I don't have a device using qcom-smd rpmsg, so it's a bit tricky to
reproduce.

Best regards,
Krzysztof