net/mlx5: Take lock with IRQs disabled to avoid deadlock

The lock in qp_table might be taken from process context or from
interrupt context. This may lead to a deadlock unless it is taken with
IRQs disabled.

Discovered by lockdep

================================
WARNING: inconsistent lock state
4.20.0-rc6
--------------------------------
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W}

python/12572 [HC1[1]:SC0[0]:HE0:SE1] takes:
00000000052a4df4 (&(&table->lock)->rlock#2){?.+.}, /0x50 [mlx5_core]
{HARDIRQ-ON-W} state was registered at:
  _raw_spin_lock+0x33/0x70
  mlx5_get_rsc+0x1a/0x50 [mlx5_core]
  mlx5_ib_eqe_pf_action+0x493/0x1be0 [mlx5_ib]
  process_one_work+0x90c/0x1820
  worker_thread+0x87/0xbb0
  kthread+0x320/0x3e0
  ret_from_fork+0x24/0x30
irq event stamp: 103928
hardirqs last  enabled at (103927): [] nk+0x1a/0x1c
hardirqs last disabled at (103928): [] unk+0x1a/0x1c
softirqs last  enabled at (103924): [] tcp_sendmsg+0x31/0x40
softirqs last disabled at (103922): [] 80

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(&table->lock)->rlock#2);

    lock(&(&table->lock)->rlock#2);

 *** DEADLOCK ***

Fixes: 032080ab ("IB/mlx5: Lock QP during page fault handling")
Signed-off-by: Moni Shoua <monis@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/qp.c

@@ -44,14 +44,15 @@ static struct mlx5_core_rsc_common *
 mlx5_get_rsc(struct mlx5_qp_table *table, u32 rsn)
 {
 	struct mlx5_core_rsc_common *common;
+	unsigned long flags;
 
-	spin_lock(&table->lock);
+	spin_lock_irqsave(&table->lock, flags);
 
 	common = radix_tree_lookup(&table->tree, rsn);
 	if (common)
 		atomic_inc(&common->refcount);
 
-	spin_unlock(&table->lock);
+	spin_unlock_irqrestore(&table->lock, flags);
 
 	return common;
 }