IB/qib: Fix potential deadlock with link down interrupt

There is a possibility of a deadlock due to the way locks are
acquired and released in qib_set_uevent_bits(). The function
qib_set_uevent_bits() is called in process context and it uses
spin_lock() and spin_unlock().  This same lock is acquired/released
in interrupt context which can lead to a deadlock when running on
the same cpu.

The fix is to replace spin_lock() and spin_unlock() with
spin_lock_irqsave() and spin_unlock_irqrestore() respectively in
qib_set_uevent_bits().
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/qib/qib_file_ops.c

@@ -1905,8 +1905,9 @@ int qib_set_uevent_bits(struct qib_pportdata *ppd, const int evtbit)
 	struct qib_ctxtdata *rcd;
 	unsigned ctxt;
 	int ret = 0;
+	unsigned long flags;
 
-	spin_lock(&ppd->dd->uctxt_lock);
+	spin_lock_irqsave(&ppd->dd->uctxt_lock, flags);
 	for (ctxt = ppd->dd->first_user_ctxt; ctxt < ppd->dd->cfgctxts;
 	     ctxt++) {
 		rcd = ppd->dd->rcd[ctxt];
@@ -1925,7 +1926,7 @@ int qib_set_uevent_bits(struct qib_pportdata *ppd, const int evtbit)
 		ret = 1;
 		break;
 	}
-	spin_unlock(&ppd->dd->uctxt_lock);
+	spin_unlock_irqrestore(&ppd->dd->uctxt_lock, flags);
 
 	return ret;
 }