[PATCH for-rc 4/4] IB/hfi1: Don't cancel unused work item

[Dennis Dalessandro <dennis.dalessandro@intel.com>]

From: Kaike Wan <kaike.wan@intel.com>

In iowait structure, two iowait_work entries were included to queue
a given object: one for normal IB operations, and the other for TID
RDMA operations. For non-TID RDMA operations, the iowait_work structure
for TID RDMA is initialized to contain a NULL function (not used).
When the QP is reset, the function iowait_cancel_work will be called
to cancel any pending work. The problem is that this function will
call cancel_work_sync for both iowait_work entries, even though the
one for TID RDMA is not used at all. Eventually, the call cascades to
__flush_work, wherein a WARN_ON will be triggered due to the fact that
work->func is NULL.

The WARN_ON was introduced in the following commit:
commit 4d43d395fed1 ("workqueue: Try to catch flush_work() without INIT_WORK().")

This patch fixes the issue by making sure that a work function is
present for TID RDMA before calling cancel_work_sync in
iowait_cancel_work.

Fixes: 5da0fc9dbf89 ("IB/hfi1: Prepare resource waits for dual leg")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
---
 drivers/infiniband/hw/hfi1/iowait.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/hfi1/iowait.c b/drivers/infiniband/hw/hfi1/iowait.c
index adb4a1b..5836fe7 100644
--- a/drivers/infiniband/hw/hfi1/iowait.c
+++ b/drivers/infiniband/hw/hfi1/iowait.c
@@ -81,7 +81,9 @@ void iowait_init(struct iowait *wait, u32 tx_limit,
 void iowait_cancel_work(struct iowait *w)
 {
 	cancel_work_sync(&iowait_get_ib_work(w)->iowork);
-	cancel_work_sync(&iowait_get_tid_work(w)->iowork);
+	/* Make sure that the iowork for TID RDMA is used */
+	if (iowait_get_tid_work(w)->iowork.func)
+		cancel_work_sync(&iowait_get_tid_work(w)->iowork);
 }
 
 /**