Always wait for txg sync when umounting dataset

Currently, when unmounting a filesystem, ZFS will only wait for
a txg sync if the dataset is dirty and not readonly. However, this
can be problematic in cases where a dataset is remounted readonly
immediately before being unmounted, which often happens when the
system is being shut down. Since encrypted datasets require that
all I/O is completed before the dataset is disowned, this issue
causes problems when write I/Os leak into the txgs after the
dataset is disowned, which can happen when sync=disabled.

While looking into fixes for this issue, it was discovered that
dsl_dataset_is_dirty() does not return B_TRUE when the dataset has
been removed from the txg dirty datasets list, but has not actually
been processed yet. Furthermore, the implementation is comletely
different from dmu_objset_is_dirty(), adding to the confusion.
Rather than relying on this function, this patch forces the umount
code path (and the remount readonly code path) to always perform a
txg sync on read-write datasets and removes the function altogether.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tom Caputi <[email protected]>
Closes #7753
Closes #7795

1 files changed, 16 insertions, 4 deletions

diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_remount.ksh b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_remount.ksh
index a83e2d117..f7a097835 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_remount.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_remount.ksh
@@ -36,8 +36,10 @@
 # 2. Verify we can (re)mount the dataset readonly/read-write
 # 3. Verify we can mount the snapshot and it's mounted readonly
 # 4. Verify we can't remount it read-write
-# 5. Re-import the pool readonly
-# 6. Verify we can't remount its filesystem read-write
+# 5. Verify we can remount a dataset readonly and unmount it with
+#    encryption=on and sync=disabled (issue #7753)
+# 6. Re-import the pool readonly
+# 7. Verify we can't remount its filesystem read-write
 #
 
 verify_runnable "both"
@@ -130,11 +132,21 @@ readonlyfs $MNTPSNAP
 checkmount $TESTSNAP 'ro'
 log_must umount $MNTPSNAP
 
-# 5. Re-import the pool readonly
+# 5. Verify we can remount a dataset readonly and unmount it with
+#    encryption=on and sync=disabled (issue #7753)
+log_must eval "echo 'password' | zfs create -o sync=disabled \
+    -o encryption=on -o keyformat=passphrase $TESTFS/crypt"
+CRYPT_MNTPFS="$(get_prop mountpoint $TESTFS/crypt)"
+log_must touch $CRYPT_MNTPFS/file.dat
+log_must mount -o remount,ro $TESTFS/crypt $CRYPT_MNTPFS
+log_must umount -f $CRYPT_MNTPFS
+zpool sync $TESTPOOL
+
+# 6. Re-import the pool readonly
 log_must zpool export $TESTPOOL
 log_must zpool import -o readonly=on $TESTPOOL
 
-# 6. Verify we can't remount its filesystem read-write
+# 7. Verify we can't remount its filesystem read-write
 readonlyfs $MNTPFS
 checkmount $TESTFS 'ro'
 log_mustnot mount -o remount,rw $MNTPFS