btrfs-progs: tests: update misc/046 to not try to mount block device into different filesystems

Since kernel commit 40426dd147ff ("btrfs: use the super_block as holder
when mounting file systems"), the kernel will not allow a block device
belonging to two different filesystems.

This means a seed device can only be mounted through either the sprouted
fs, or the seed device, not both at the same time.

Although a seed device can still be shared between different sprouted
fs, only one of those fs can be mounted.

Considering the extra benefit (extra protection, better device events
handling), it's worthy to do the kernel behavior change.

Update the test case to follow the new limits.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>

Author: adam900710

tests/misc-tests/046-seed-multi-mount/test.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Verify that a seeding device can be mounted several times
+# Verify that a seeding device can be shared by different sprout filesystems.
 
 source "$TEST_TOP/common" || exit
 
@@ -74,21 +74,20 @@ nextdevice() {
 	if [ "$md5sum" != "$md5sum2" ]; then
 		_fail "file contents not same after remount"
 	fi
+	# Unmount the new device so that the seed device won't be mounted
+	# when the sprout fs is already mounted.
+	# This is to compensate for the new v6.17 kernel, as each different
+	# fs will have different holder for a block device, and a single block
+	# device can not belong to different mounted filesystems.
+	run_check_umount_test_dev
 }
 
-# Keep previous device(s) mounted, create a new filesystem from the seeding device
+# Create a new filesystem from the seeding device, with previous devices unmounted.
 nextdevice 2
 nextdevice 3
 nextdevice 4
 nextdevice 5
 
-# Final umount
-# Skip seeding device, loop device 1,
-run_check $SUDO_HELPER umount ${loopdevs[2]}
-run_check $SUDO_HELPER umount ${loopdevs[3]}
-run_check $SUDO_HELPER umount ${loopdevs[4]}
-run_check $SUDO_HELPER umount ${loopdevs[5]}
-
 cleanup_loopdevs
 
 rm -rf -- mnt[0-9]