diff --git a/fs_mgr/libsnapshot/snapshot.cpp b/fs_mgr/libsnapshot/snapshot.cpp
index f4584d2..e6e17bd 100644
--- a/fs_mgr/libsnapshot/snapshot.cpp
+++ b/fs_mgr/libsnapshot/snapshot.cpp
@@ -668,9 +668,15 @@
 bool SnapshotManager::UnmapSnapshot(LockedFile* lock, const std::string& name) {
     CHECK(lock);
 
-    if (!DeleteDeviceIfExists(name)) {
-        LOG(ERROR) << "Could not delete snapshot device: " << name;
-        return false;
+    if (UpdateUsesUserSnapshots(lock)) {
+        if (!UnmapUserspaceSnapshotDevice(lock, name)) {
+            return false;
+        }
+    } else {
+        if (!DeleteDeviceIfExists(name)) {
+            LOG(ERROR) << "Could not delete snapshot device: " << name;
+            return false;
+        }
     }
     return true;
 }
@@ -2429,10 +2435,8 @@
                                                  const std::string& target_partition_name) {
     CHECK(lock);
 
-    if (!UpdateUsesUserSnapshots(lock)) {
-        if (!UnmapSnapshot(lock, target_partition_name)) {
-            return false;
-        }
+    if (!UnmapSnapshot(lock, target_partition_name)) {
+        return false;
     }
 
     if (!UnmapCowDevices(lock, target_partition_name)) {
@@ -2530,16 +2534,10 @@
     CHECK(lock);
     if (!EnsureImageManager()) return false;
 
-    if (UpdateUsesCompression(lock)) {
-        if (UpdateUsesUserSnapshots(lock)) {
-            if (!UnmapUserspaceSnapshotDevice(lock, name)) {
-                return false;
-            }
-        } else {
-            auto dm_user_name = GetDmUserCowName(name, GetSnapshotDriver(lock));
-            if (!UnmapDmUserDevice(dm_user_name)) {
-                return false;
-            }
+    if (UpdateUsesCompression(lock) && !UpdateUsesUserSnapshots(lock)) {
+        auto dm_user_name = GetDmUserCowName(name, GetSnapshotDriver(lock));
+        if (!UnmapDmUserDevice(dm_user_name)) {
+            return false;
         }
     }
 
diff --git a/fs_mgr/libsnapshot/snapshot_reader_test.cpp b/fs_mgr/libsnapshot/snapshot_reader_test.cpp
index 078f16e..9adc655 100644
--- a/fs_mgr/libsnapshot/snapshot_reader_test.cpp
+++ b/fs_mgr/libsnapshot/snapshot_reader_test.cpp
@@ -155,8 +155,8 @@
     }
 
     std::string MakeXorBlockString() {
-        std::string data(100, -1);
-        data.resize(kBlockSize, 0);
+        std::string data(kBlockSize, 0);
+        memset(data.data(), 0xff, 100);
         return data;
     }
 
diff --git a/fs_mgr/libsnapshot/snapshot_test.cpp b/fs_mgr/libsnapshot/snapshot_test.cpp
index f1d76e7..7001b9a 100644
--- a/fs_mgr/libsnapshot/snapshot_test.cpp
+++ b/fs_mgr/libsnapshot/snapshot_test.cpp
@@ -897,9 +897,9 @@
         ASSERT_NE(nullptr, metadata);
         ASSERT_TRUE(UpdatePartitionTable(*opener_, "super", *metadata.get(), 0));
 
-        // Map source partitions. Additionally, map sys_b to simulate system_other after flashing.
+        // Map source partitions.
         std::string path;
-        for (const auto& name : {"sys_a", "vnd_a", "prd_a", "sys_b"}) {
+        for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
             ASSERT_TRUE(CreateLogicalPartition(
                     CreateLogicalPartitionParams{
                             .block_device = fake_super,
@@ -2215,6 +2215,8 @@
 TEST_F(SnapshotUpdateTest, CancelOnTargetSlot) {
     AddOperationForPartitions();
 
+    ASSERT_TRUE(UnmapAll());
+
     // Execute the update from B->A.
     test_device->set_slot_suffix("_b");
     ASSERT_TRUE(sm->BeginUpdate());
diff --git a/fs_mgr/libsnapshot/snapuserd/Android.bp b/fs_mgr/libsnapshot/snapuserd/Android.bp
index 93b0f7c..4d86007 100644
--- a/fs_mgr/libsnapshot/snapuserd/Android.bp
+++ b/fs_mgr/libsnapshot/snapuserd/Android.bp
@@ -61,12 +61,12 @@
         "dm-snapshot-merge/snapuserd_worker.cpp",
         "dm-snapshot-merge/snapuserd_readahead.cpp",
         "snapuserd_daemon.cpp",
-	"snapuserd_buffer.cpp",
-	"user-space-merge/snapuserd_core.cpp",
-	"user-space-merge/snapuserd_dm_user.cpp",
-	"user-space-merge/snapuserd_merge.cpp",
-	"user-space-merge/snapuserd_readahead.cpp",
-	"user-space-merge/snapuserd_transitions.cpp",
+        "snapuserd_buffer.cpp",
+        "user-space-merge/snapuserd_core.cpp",
+        "user-space-merge/snapuserd_dm_user.cpp",
+        "user-space-merge/snapuserd_merge.cpp",
+        "user-space-merge/snapuserd_readahead.cpp",
+        "user-space-merge/snapuserd_transitions.cpp",
         "user-space-merge/snapuserd_server.cpp",
     ],
 
@@ -95,7 +95,14 @@
     init_rc: [
         "snapuserd.rc",
     ],
+
+    // snapuserd is started during early boot by first-stage init. At that
+    // point, /system is mounted using the "dm-user" device-mapper kernel
+    // module. dm-user routes all I/O to userspace to be handled by
+    // snapuserd, which would lead to deadlock if we had to handle page
+    // faults for its code pages.
     static_executable: true,
+
     system_shared_libs: [],
     ramdisk_available: true,
     vendor_ramdisk_available: true,
@@ -111,7 +118,7 @@
         "dm-snapshot-merge/cow_snapuserd_test.cpp",
         "dm-snapshot-merge/snapuserd.cpp",
         "dm-snapshot-merge/snapuserd_worker.cpp",
-	"snapuserd_buffer.cpp",
+        "snapuserd_buffer.cpp",
     ],
     cflags: [
         "-Wall",