[PATCH 3.16 046/129] scsi: target/iscsi: Avoid iscsit_release_commands_from_conn() deadlock

[Ben Hutchings]

3.16.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Bart Van Assche <bvanassche@xxxxxxx>

commit 32e36bfbcf31452a854263e7c7f32fbefc4b44d8 upstream.

When using SCSI passthrough in combination with the iSCSI target driver
then cmd->t_state_lock may be obtained from interrupt context. Hence, all
code that obtains cmd->t_state_lock from thread context must disable
interrupts first. This patch avoids that lockdep reports the following:

WARNING: inconsistent lock state
4.18.0-dbg+ #1 Not tainted
--------------------------------
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
iscsi_ttx/1800 [HC1[1]:SC0[2]:HE0:SE0] takes:
000000006e7b0ceb (&(&cmd->t_state_lock)->rlock){?...}, at: target_complete_cmd+0x47/0x2c0 [target_core_mod]
{HARDIRQ-ON-W} state was registered at:
 lock_acquire+0xd2/0x260
 _raw_spin_lock+0x32/0x50
 iscsit_close_connection+0x97e/0x1020 [iscsi_target_mod]
 iscsit_take_action_for_connection_exit+0x108/0x200 [iscsi_target_mod]
 iscsi_target_rx_thread+0x180/0x190 [iscsi_target_mod]
 kthread+0x1cf/0x1f0
 ret_from_fork+0x24/0x30
irq event stamp: 1281
hardirqs last  enabled at (1279): [<ffffffff970ade79>] __local_bh_enable_ip+0xa9/0x160
hardirqs last disabled at (1281): [<ffffffff97a008a5>] interrupt_entry+0xb5/0xd0
softirqs last  enabled at (1278): [<ffffffff977cd9a1>] lock_sock_nested+0x51/0xc0
softirqs last disabled at (1280): [<ffffffffc07a6e04>] ip6_finish_output2+0x124/0xe40 [ipv6]

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

      CPU0
      ----
 lock(&(&cmd->t_state_lock)->rlock);
 <Interrupt>
   lock(&(&cmd->t_state_lock)->rlock);

--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -4201,9 +4201,9 @@ static void iscsit_release_commands_from
 		struct se_cmd *se_cmd = &cmd->se_cmd;
 
 		if (se_cmd->se_tfo != NULL) {
-			spin_lock(&se_cmd->t_state_lock);
+			spin_lock_irq(&se_cmd->t_state_lock);
 			se_cmd->transport_state |= CMD_T_FABRIC_STOP;
-			spin_unlock(&se_cmd->t_state_lock);
+			spin_unlock_irq(&se_cmd->t_state_lock);
 		}
 	}
 	spin_unlock_bh(&conn->cmd_lock);