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

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