scsi: ipr: Fix scsi-mq lockdep issue

Fixes the following lockdep warning that can occur when scsi-mq is
enabled with ipr due to ipr calling scsi_unblock_requests from irq
context. The fix is to move the call to scsi_unblock_requests to ipr's
existing workqueue.

stack backtrace:
CPU: 28 PID: 0 Comm: swapper/28 Not tainted 4.13.0-rc2-gcc6x-gf74c89b #1
Call Trace:
[c000001fffe97550] [c000000000b50818] dump_stack+0xe8/0x160 (unreliable)
[c000001fffe97590] [c0000000001586d0] print_usage_bug+0x2d0/0x390
[c000001fffe97640] [c000000000158f34] mark_lock+0x7a4/0x8e0
[c000001fffe976f0] [c00000000015a000] __lock_acquire+0x6a0/0x1a70
[c000001fffe97860] [c00000000015befc] lock_acquire+0xec/0x2e0
[c000001fffe97930] [c000000000b71514] _raw_spin_lock+0x44/0x70
[c000001fffe97960] [c0000000005b60f4] blk_mq_sched_dispatch_requests+0xa4/0x2a0
[c000001fffe979c0] [c0000000005acac0] __blk_mq_run_hw_queue+0x100/0x2c0
[c000001fffe97a00] [c0000000005ad478] __blk_mq_delay_run_hw_queue+0x118/0x130
[c000001fffe97a40] [c0000000005ad61c] blk_mq_start_hw_queues+0x6c/0xa0
[c000001fffe97a80] [c000000000797aac] scsi_kick_queue+0x2c/0x60
[c000001fffe97aa0] [c000000000797cf0] scsi_run_queue+0x210/0x360
[c000001fffe97b10] [c00000000079b888] scsi_run_host_queues+0x48/0x80
[c000001fffe97b40] [c0000000007b6090] ipr_ioa_bringdown_done+0x70/0x1e0
[c000001fffe97bc0] [c0000000007bc860] ipr_reset_ioa_job+0x80/0xf0
[c000001fffe97bf0] [c0000000007b4d50] ipr_reset_timer_done+0xd0/0x100
[c000001fffe97c30] [c0000000001937bc] call_timer_fn+0xdc/0x4b0
[c000001fffe97cf0] [c000000000193d08] expire_timers+0x178/0x330
[c000001fffe97d60] [c0000000001940c8] run_timer_softirq+0xb8/0x120
[c000001fffe97de0] [c000000000b726a8] __do_softirq+0x168/0x6d8
[c000001fffe97ef0] [c0000000000df2c8] irq_exit+0x108/0x150
[c000001fffe97f10] [c000000000017bf4] __do_irq+0x2a4/0x4a0
[c000001fffe97f90] [c00000000002da50] call_do_irq+0x14/0x24
[c0000007fad93aa0] [c000000000017e8c] do_IRQ+0x9c/0x140
[c0000007fad93af0] [c000000000008b98] hardware_interrupt_common+0x138/0x140

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ipr.c

@@ -3351,6 +3351,16 @@ static void ipr_worker_thread(struct work_struct *work)
 		return;
 	}
 
+	if (ioa_cfg->scsi_unblock) {
+		ioa_cfg->scsi_unblock = 0;
+		ioa_cfg->scsi_blocked = 0;
+		spin_unlock_irqrestore(ioa_cfg->host->host_lock, lock_flags);
+		scsi_unblock_requests(ioa_cfg->host);
+		spin_lock_irqsave(ioa_cfg->host->host_lock, lock_flags);
+		if (ioa_cfg->scsi_blocked)
+			scsi_block_requests(ioa_cfg->host);
+	}
+
 	if (!ioa_cfg->scan_enabled) {
 		spin_unlock_irqrestore(ioa_cfg->host->host_lock, lock_flags);
 		return;
@@ -7211,9 +7221,8 @@ static int ipr_ioa_bringdown_done(struct ipr_cmnd *ipr_cmd)
 	ENTER;
 	if (!ioa_cfg->hrrq[IPR_INIT_HRRQ].removing_ioa) {
 		ipr_trace;
-		spin_unlock_irq(ioa_cfg->host->host_lock);
-		scsi_unblock_requests(ioa_cfg->host);
-		spin_lock_irq(ioa_cfg->host->host_lock);
+		ioa_cfg->scsi_unblock = 1;
+		schedule_work(&ioa_cfg->work_q);
 	}
 
 	ioa_cfg->in_reset_reload = 0;
@@ -7287,13 +7296,7 @@ static int ipr_ioa_reset_done(struct ipr_cmnd *ipr_cmd)
 	list_add_tail(&ipr_cmd->queue, &ipr_cmd->hrrq->hrrq_free_q);
 	wake_up_all(&ioa_cfg->reset_wait_q);
 
-	spin_unlock(ioa_cfg->host->host_lock);
-	scsi_unblock_requests(ioa_cfg->host);
-	spin_lock(ioa_cfg->host->host_lock);
-
-	if (!ioa_cfg->hrrq[IPR_INIT_HRRQ].allow_cmds)
-		scsi_block_requests(ioa_cfg->host);
-
+	ioa_cfg->scsi_unblock = 1;
 	schedule_work(&ioa_cfg->work_q);
 	LEAVE;
 	return IPR_RC_JOB_RETURN;
@@ -9249,8 +9252,11 @@ static void _ipr_initiate_ioa_reset(struct ipr_ioa_cfg *ioa_cfg,
 		spin_unlock(&ioa_cfg->hrrq[i]._lock);
 	}
 	wmb();
-	if (!ioa_cfg->hrrq[IPR_INIT_HRRQ].removing_ioa)
+	if (!ioa_cfg->hrrq[IPR_INIT_HRRQ].removing_ioa) {
+		ioa_cfg->scsi_unblock = 0;
+		ioa_cfg->scsi_blocked = 1;
 		scsi_block_requests(ioa_cfg->host);
+	}
 
 	ipr_cmd = ipr_get_free_ipr_cmnd(ioa_cfg);
 	ioa_cfg->reset_cmd = ipr_cmd;
@@ -9306,9 +9312,8 @@ static void ipr_initiate_ioa_reset(struct ipr_ioa_cfg *ioa_cfg,
 			wake_up_all(&ioa_cfg->reset_wait_q);
 
 			if (!ioa_cfg->hrrq[IPR_INIT_HRRQ].removing_ioa) {
-				spin_unlock_irq(ioa_cfg->host->host_lock);
-				scsi_unblock_requests(ioa_cfg->host);
-				spin_lock_irq(ioa_cfg->host->host_lock);
+				ioa_cfg->scsi_unblock = 1;
+				schedule_work(&ioa_cfg->work_q);
 			}
 			return;
 		} else {

drivers/scsi/ipr.h

@@ -1488,6 +1488,8 @@ struct ipr_ioa_cfg {
 	u8 cfg_locked:1;
 	u8 clear_isr:1;
 	u8 probe_done:1;
+	u8 scsi_unblock:1;
+	u8 scsi_blocked:1;
 
 	u8 revid;