[PATCH] IB/hfi1: Fix potential deadlock on &irq_src_lock and &dd->uctxt_lock

[Chengfeng Ye <dg573847474@gmail.com>]

handle_receive_interrupt_napi_sp() running inside interrupt handler
could introduce inverse lock ordering between &dd->irq_src_lock
and &dd->uctxt_lock, if read_mod_write() is preempted by the isr.

          [CPU0]                                        |          [CPU1]
hfi1_ipoib_dev_open()                                   |
--> hfi1_netdev_enable_queues()                         |
--> enable_queues(rx)                                   |
--> hfi1_rcvctrl()                                      |
--> set_intr_bits()                                     |
--> read_mod_write()                                    |
--> spin_lock(&dd->irq_src_lock)                        |
                                                        | hfi1_poll()
                                                        | --> poll_next()
                                                        | --> spin_lock_irq(&dd->uctxt_lock)
                                                        |
                                                        | --> hfi1_rcvctrl()
                                                        | --> set_intr_bits()
                                                        | --> read_mod_write()
                                                        | --> spin_lock(&dd->irq_src_lock)
<interrupt>                                             |
   --> handle_receive_interrupt_napi_sp()               |
   --> set_all_fastpath()                               |
   --> hfi1_rcd_get_by_index()                          |
   --> spin_lock_irqsave(&dd->uctxt_lock)               |

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

To prevent the potential deadlock, the patch use spin_lock_irqsave()
on &dd->irq_src_lock inside read_mod_write() to prevent the possible
deadlock scenario.

Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
 drivers/infiniband/hw/hfi1/chip.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/chip.c b/drivers/infiniband/hw/hfi1/chip.c
index 0814291a0412..9b542f7c6c11 100644
--- a/drivers/infiniband/hw/hfi1/chip.c
+++ b/drivers/infiniband/hw/hfi1/chip.c
@@ -13185,15 +13185,16 @@ static void read_mod_write(struct hfi1_devdata *dd, u16 src, u64 bits,
 {
 	u64 reg;
 	u16 idx = src / BITS_PER_REGISTER;
+	unsigned long flags;
 
-	spin_lock(&dd->irq_src_lock);
+	spin_lock_irqsave(&dd->irq_src_lock, flags);
 	reg = read_csr(dd, CCE_INT_MASK + (8 * idx));
 	if (set)
 		reg |= bits;
 	else
 		reg &= ~bits;
 	write_csr(dd, CCE_INT_MASK + (8 * idx), reg);
-	spin_unlock(&dd->irq_src_lock);
+	spin_unlock_irqrestore(&dd->irq_src_lock, flags);
 }
 
 /**
-- 
2.17.1