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

Marek Szyprowski
2022-04-29T12:29:51Z

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@linaro.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

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