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

[Mao Jinlong]

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 at quicinc.com>
Signed-off-by: Mao Jinlong <quic_jinlmao at 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;
-- 
2.17.1