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

[Krzysztof Kozlowski]

On 29/04/2022 14:29, Marek Szyprowski wrote:
> Hi Krzysztof,
> 
> 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/

-----

diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
index 3e81642238d2..1e2ad944e2ec 100644
--- a/drivers/rpmsg/rpmsg_internal.h
+++ b/drivers/rpmsg/rpmsg_internal.h
@@ -102,11 +102,7 @@ static inline int
rpmsg_ctrldev_register_device(struct rpmsg_device *rpdev)
        if (ret)
                return ret;

-       ret = rpmsg_register_device(rpdev);
-       if (ret)
-               kfree(rpdev->driver_override);
-
-       return ret;
+       return rpmsg_register_device(rpdev);
 }

 #endif
diff --git a/drivers/rpmsg/rpmsg_ns.c b/drivers/rpmsg/rpmsg_ns.c
index 8eb8f328237e..f26078467899 100644
--- a/drivers/rpmsg/rpmsg_ns.c
+++ b/drivers/rpmsg/rpmsg_ns.c
@@ -31,11 +31,7 @@ int rpmsg_ns_register_device(struct rpmsg_device *rpdev)
        rpdev->src = RPMSG_NS_ADDR;
        rpdev->dst = RPMSG_NS_ADDR;

-       ret = rpmsg_register_device(rpdev);
-       if (ret)
-               kfree(rpdev->driver_override);
-
-       return ret;
+       return rpmsg_register_device(rpdev);
 }
 EXPORT_SYMBOL(rpmsg_ns_register_device);