[PATCH] workqueue: fix potential reentrancy issue

[Libin <huawei.libin@huawei.com>]

From: Li Bin <huawei.libin@huawei.com>

When one work starts execution, the high bits of work's data contain
pool ID. It can represent a maximum of WORK_OFFQ_POOL_NONE. Pool ID
is assigned WORK_OFFQ_POOL_NONE when the work being initialized
indicating that no pool is associated and get_work_pool() uses it to
check the associated pool. So if worker_pool_assign_id() assigns a
ID greater than or equal WORK_OFFQ_POOL_NONE to a pool, it may break
the non-reentrance guarantee.

This patch fix this issue by modifying the worker_pool_assign_id()
function to add the WORK_OFFQ_POOL_NONE check condition.

Signed-off-by: Li Bin <huawei.libin@huawei.com>
---
 kernel/workqueue.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 41019b1..97d9ff7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -518,7 +518,14 @@ static inline void debug_work_activate(struct work_struct *work) { }
 static inline void debug_work_deactivate(struct work_struct *work) { }
 #endif
 
-/* allocate ID and assign it to @pool */
+/**
+ * worker_pool_assign_id - allocate ID and assing it to @pool
+ * @pool: the pool pointer of interest
+ *
+ * Return 0 if ID assigned successful.
+ * Return non-zero if the allocation fails or the ID number out of
+ * %WORK_OFFQ_POOL_NONE range.
+ */
 static int worker_pool_assign_id(struct worker_pool *pool)
 {
 	int ret;
@@ -526,6 +533,8 @@ static int worker_pool_assign_id(struct worker_pool *pool)
 	lockdep_assert_held(&wq_pool_mutex);
 
 	ret = idr_alloc(&worker_pool_idr, pool, 0, 0, GFP_KERNEL);
+	if (ret >= WORK_OFFQ_POOL_NONE)
+		return ret;
 	if (ret >= 0) {
 		pool->id = ret;
 		return 0;
-- 
1.8.2.1