scsi: megaraid_sas: Fix for a potential deadlock

This fixes a 'possible circular locking dependency detected' warning
      CPU0                    CPU1
      ----                    ----
 lock(&instance->reset_mutex);
                              lock(&shost->scan_mutex);
                              lock(&instance->reset_mutex);
 lock(&shost->scan_mutex);

Fix this by temporarily releasing the reset_mutex.

Signed-off-by: Tomas Henzl <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Acked-by: Chandrakanth Patil <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: thenzl

drivers/scsi/megaraid/megaraid_sas_base.c

@@ -8907,8 +8907,11 @@ megasas_aen_polling(struct work_struct *work)
 						   (ld_target_id / MEGASAS_MAX_DEV_PER_CHANNEL),
 						   (ld_target_id % MEGASAS_MAX_DEV_PER_CHANNEL),
 						   0);
-			if (sdev1)
+			if (sdev1) {
+				mutex_unlock(&instance->reset_mutex);
 				megasas_remove_scsi_device(sdev1);
+				mutex_lock(&instance->reset_mutex);
+			}
 
 			event_type = SCAN_VD_CHANNEL;
 			break;