From: Stefan Haberland <sth@linux.ibm.com>
Date: Thu, 17 Dec 2020 16:59:05 +0100
Subject: s390/dasd: prevent inconsistent LCU device data
Git-commit: a29ea01653493b94ea12bb2b89d1564a265081b6
Patch-mainline: v5.11-rc1
References: bsc#1181170 LTC#190915

Prevent _lcu_update from adding a device to a pavgroup if the LCU still
requires an update. The data is not reliable any longer and in parallel
devices might have been moved on the lists already.
This might lead to list corruptions or invalid PAV grouping.
Only add devices to a pavgroup if the LCU is up to date. Additional steps
are taken by the scheduled lcu update.

Fixes: 8e09f21574ea ("[S390] dasd: add hyper PAV support to DASD device driver, part 1")
Cc: stable@vger.kernel.org
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/s390/block/dasd_alias.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/s390/block/dasd_alias.c
+++ b/drivers/s390/block/dasd_alias.c
@@ -510,6 +510,14 @@ static int _lcu_update(struct dasd_devic
 		return rc;
 
 	spin_lock_irqsave(&lcu->lock, flags);
+	/*
+	 * there is another update needed skip the remaining handling
+	 * the data might already be outdated
+	 * but especially do not add the device to an LCU with pending
+	 * update
+	 */
+	if (lcu->flags & NEED_UAC_UPDATE)
+		goto out;
 	lcu->pav = NO_PAV;
 	for (i = 0; i < MAX_DEVICES_PER_LCU; ++i) {
 		switch (lcu->uac->unit[i].ua_type) {
@@ -528,6 +536,7 @@ static int _lcu_update(struct dasd_devic
 				 alias_list) {
 		_add_device_to_lcu(lcu, device, refdev);
 	}
+out:
 	spin_unlock_irqrestore(&lcu->lock, flags);
 	return 0;
 }