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

[Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>]

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?

> ---
>   drivers/rpmsg/rpmsg_internal.h | 13 +++++++++++--
>   drivers/rpmsg/rpmsg_ns.c       | 14 ++++++++++++--
>   include/linux/rpmsg.h          |  6 ++++--
>   3 files changed, 27 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
> index d4b23fd019a8..3e81642238d2 100644
> --- a/drivers/rpmsg/rpmsg_internal.h
> +++ b/drivers/rpmsg/rpmsg_internal.h
> @@ -94,10 +94,19 @@ int rpmsg_release_channel(struct rpmsg_device *rpdev,
>    */
>   static inline int rpmsg_ctrldev_register_device(struct rpmsg_device *rpdev)
>   {
> +	int ret;
> +
>   	strcpy(rpdev->id.name, "rpmsg_ctrl");
> -	rpdev->driver_override = "rpmsg_ctrl";
> +	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
> +				  rpdev->id.name, strlen(rpdev->id.name));
> +	if (ret)
> +		return ret;
> +
> +	ret = rpmsg_register_device(rpdev);
> +	if (ret)
> +		kfree(rpdev->driver_override);
>   
> -	return rpmsg_register_device(rpdev);
> +	return ret;
>   }
>   
>   #endif
> diff --git a/drivers/rpmsg/rpmsg_ns.c b/drivers/rpmsg/rpmsg_ns.c
> index 762ff1ae279f..8eb8f328237e 100644
> --- a/drivers/rpmsg/rpmsg_ns.c
> +++ b/drivers/rpmsg/rpmsg_ns.c
> @@ -20,12 +20,22 @@
>    */
>   int rpmsg_ns_register_device(struct rpmsg_device *rpdev)
>   {
> +	int ret;
> +
>   	strcpy(rpdev->id.name, "rpmsg_ns");
> -	rpdev->driver_override = "rpmsg_ns";
> +	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
> +				  rpdev->id.name, strlen(rpdev->id.name));
> +	if (ret)
> +		return ret;
> +
>   	rpdev->src = RPMSG_NS_ADDR;
>   	rpdev->dst = RPMSG_NS_ADDR;
>   
> -	return rpmsg_register_device(rpdev);
> +	ret = rpmsg_register_device(rpdev);
> +	if (ret)
> +		kfree(rpdev->driver_override);
> +
> +	return ret;
>   }
>   EXPORT_SYMBOL(rpmsg_ns_register_device);
>   
> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> index 02fa9116cd60..20c8cd1cde21 100644
> --- a/include/linux/rpmsg.h
> +++ b/include/linux/rpmsg.h
> @@ -41,7 +41,9 @@ struct rpmsg_channel_info {
>    * rpmsg_device - device that belong to the rpmsg bus
>    * @dev: the device struct
>    * @id: device id (used to match between rpmsg drivers and devices)
> - * @driver_override: driver name to force a match
> + * @driver_override: driver name to force a match; do not set directly,
> + *                   because core frees it; use driver_set_override() to
> + *                   set or clear it.
>    * @src: local address
>    * @dst: destination address
>    * @ept: the rpmsg endpoint of this channel
> @@ -51,7 +53,7 @@ struct rpmsg_channel_info {
>   struct rpmsg_device {
>   	struct device dev;
>   	struct rpmsg_device_id id;
> -	char *driver_override;
> +	const char *driver_override;
>   	u32 src;
>   	u32 dst;
>   	struct rpmsg_endpoint *ept;

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland