[Devel] [PATCH RHEL7 COMMIT] ploop: Print mounted sb information on busy stop fail

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.11.1.vz7.172.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.11.1.vz7.172.10
------>
commit 4e746201d6d14883f24154f879b0b148856c5733
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Sat Jan 30 14:42:31 2021 +0300

    ploop: Print mounted sb information on busy stop fail
    
    Add a debug into error message.
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 drivers/block/ploop/dev.c | 51 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/drivers/block/ploop/dev.c b/drivers/block/ploop/dev.c
index 320a5d5..61adcd0 100644
--- a/drivers/block/ploop/dev.c
+++ b/drivers/block/ploop/dev.c
@@ -3751,6 +3751,45 @@ out:
 	return sb;
 }
 
+/*
+ * Returns true in case of there is mounted sb.
+ * This can't handle nested dm devices stacks.
+ */
+static bool ploop_has_active_sb(struct ploop_device *plo,
+				struct block_device *bd)
+{
+	struct gendisk *disk = plo->disk;
+	struct block_device *bdev = NULL;
+	struct super_block *sb = NULL;
+	int i;
+
+	bdev = ploop_get_dm_crypt_bdev(plo);
+	if (bdev) {
+		sb = get_super(bdev);
+		goto out;
+	}
+
+	for (i = 0; i <= bd->bd_part_count; i++) {
+		bdev = bdget_disk(disk, i);
+		if (!bdev)
+			break;
+
+		sb = get_super(bdev);
+		if (sb)
+			break;
+
+		bdput(bdev);
+		bdev = NULL;
+	}
+
+out:
+	if (sb)
+		drop_super(sb);
+	if (bdev)
+		bdput(bdev);
+	return sb != NULL;
+}
+
 static int ploop_snapshot(struct ploop_device * plo, unsigned long arg,
 			  struct block_device * bdev)
 {
@@ -4354,9 +4393,15 @@ static int ploop_stop(struct ploop_device * plo, struct block_device *bdev)
 	}
 
 	if (bdev->bd_contains->bd_holders) {
-		if (printk_ratelimit())
-			printk(KERN_INFO "stop ploop%d failed (holders=%d)\n",
-			       plo->index, bdev->bd_contains->bd_holders);
+		if (printk_ratelimit()) {
+			int holders, active;
+			holders = bdev->bd_contains->bd_holders;
+			mutex_unlock(&plo->ctl_mutex);
+			active = ploop_has_active_sb(plo, bdev);
+			pr_info("stop ploop%d failed (holders=%d, sb=%d)\n",
+				plo->index, holders, active);
+			mutex_lock(&plo->ctl_mutex);
+		}
 		return -EBUSY;
 	}