[PATCH] scsi: qla4xxx: fix potential deadlock on frwd/back lock

[Chengfeng Ye]

iscsi_complete_pdu() is called by several rx callback, under
softirq context. Thus the callsite of it inside qla4xxx_task_work()
should better disable bottom half, as work queue is executed under
process context, it needs to protect race with softirq context
locking to avoid deadlock.

<potential deadlock #1>
qla4xxx_task_work()
--> iscsi_complete_pdu()
--> spin_lock(&conn->session->back_lock);
<interrupt>
   --> iscsi_tcp_data_recv_done()
   --> iscsi_complete_pdu()
   --> spin_lock(&conn->session->back_lock) (deadlock)

<potential deadlock #2>
qla4xxx_task_work()
--> iscsi_complete_pdu()
--> __iscsi_complete_pdu()
--> spin_lock(&conn->session->frwd_lock)
<interrupt>
   --> iscsi_tcp_data_recv_done()
   --> iscsi_complete_pdu()
   --> __iscsi_complete_pdu()
   --> spin_lock(&conn->session->frwd_lock) (deadlock)

This flaw was found by an experimental static analysis tool I am
developing for irq-related deadlock.

To avoid the problem, disable bh inside qla4xxx_task_work() before
calling iscsi_complete_pdu().

Signed-off-by: Chengfeng Ye <dg573847474@xxxxxxxxx>
---
 drivers/scsi/qla4xxx/ql4_os.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/scsi/qla4xxx/ql4_os.c b/drivers/scsi/qla4xxx/ql4_os.c
index 675332e49a7b..c60781148e6c 100644
--- a/drivers/scsi/qla4xxx/ql4_os.c
+++ b/drivers/scsi/qla4xxx/ql4_os.c
@@ -3382,7 +3382,9 @@ static void qla4xxx_task_work(struct work_struct *wdata)
 		hdr->itt = itt;
 		data = task_data->resp_buffer + hdr_len;
 		data_len = task_data->resp_len - hdr_len;
+		local_bh_disable();
 		iscsi_complete_pdu(conn, hdr, data, data_len);
+		local_bh_enable();
 		break;
 	default:
 		ql4_printk(KERN_ERR, ha, "Passthru failed status = 0x%x\n",
-- 
2.17.1