Re: [PATCH] stm class: Fix double add issue when store source_link

[Jinlong Mao <quic_jinlmao@quicinc.com>]

Hi Reviewers,

Could you please help to review this patch ?

Thanks

Jinlong Mao

On 4/18/2022 7:46 PM, Mao Jinlong wrote:
> If two threads store the same stm device to stm_source_link
> at the same time when stm->link_list is empty, it is possible
> that stm_source_link_add will be called for both of these two
> threads. Then double add issue below will happen. Add mutex
> lock for stm_source_link drop and stm_source_link add to avoid
> this race condition.
>
> [ 12.386579][ T1024] list_add double add: new=ffffff87b73ebd90,
> prev=ffffff87b73ebd90, next=ffffffc012737700.
> [ 12.386657][ T1024] -----------[ cut here ]-----------
> [ 12.386671][ T1024] kernel BUG at lib/list_debug.c:31!
> [ 12.388845][ T1024] CPU: 2 PID: 1024 Comm: sh
> [ 12.389162][ T1024] Call trace:
> [ 12.389174][ T1024] __list_add_valid+0x68/0x98
> [ 12.389199][ T1024] stm_source_link_store+0xcc/0x314 [stm_core]
> [ 12.389213][ T1024] dev_attr_store+0x38/0x8c
> [ 12.389228][ T1024] sysfs_kf_write+0xa0/0x100
> [ 12.389239][ T1024] kernfs_fop_write_iter+0x1b0/0x2f8
> [ 12.389253][ T1024] vfs_write+0x300/0x37c
> [ 12.389264][ T1024] ksys_write+0x84/0x12c
>
> Signed-off-by: Yuanfang Zhang <quic_yuanfang@quicinc.com>
> Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
> ---
>   drivers/hwtracing/stm/core.c | 7 ++++++-
>   drivers/hwtracing/stm/stm.h  | 1 +
>   2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> index 2712e699ba08..e73ac961acb2 100644
> --- a/drivers/hwtracing/stm/core.c
> +++ b/drivers/hwtracing/stm/core.c
> @@ -1171,11 +1171,14 @@ static ssize_t stm_source_link_store(struct device *dev,
>   	struct stm_device *link;
>   	int err;
>   
> +	mutex_lock(&src->link_mutex);
>   	stm_source_link_drop(src);
>   
>   	link = stm_find_device(buf);
> -	if (!link)
> +	if (!link) {
> +		mutex_lock(&src->link_mutex);
>   		return -EINVAL;
> +	}
>   
>   	pm_runtime_get(&link->dev);
>   
> @@ -1185,6 +1188,7 @@ static ssize_t stm_source_link_store(struct device *dev,
>   		/* matches the stm_find_device() above */
>   		stm_put_device(link);
>   	}
> +	mutex_unlock(&src->link_mutex);
>   
>   	return err ? : count;
>   }
> @@ -1251,6 +1255,7 @@ int stm_source_register_device(struct device *parent,
>   
>   	stm_output_init(&src->output);
>   	spin_lock_init(&src->link_lock);
> +	mutex_init(&src->link_mutex);
>   	INIT_LIST_HEAD(&src->link_entry);
>   	src->data = data;
>   	data->src = src;
> diff --git a/drivers/hwtracing/stm/stm.h b/drivers/hwtracing/stm/stm.h
> index a9be49fc7a6b..60b814cc00e0 100644
> --- a/drivers/hwtracing/stm/stm.h
> +++ b/drivers/hwtracing/stm/stm.h
> @@ -79,6 +79,7 @@ void stm_put_device(struct stm_device *stm);
>   struct stm_source_device {
>   	struct device		dev;
>   	struct stm_source_data	*data;
> +	struct mutex		link_mutex;
>   	spinlock_t		link_lock;
>   	struct stm_device __rcu	*link;
>   	struct list_head	link_entry;