squashfs, overlay: unmount the rom once nothing is holding it

package/batocera/core/batocera-configgen/configgen/configgen/emulatorlauncher.py

@@ -184,15 +184,17 @@ def start_rom(args: argparse.Namespace, maxnbplayers: int, rom: Path, original_r
 
                 # run the emulator
                 _evmapy_instance = evmapy(systemName, system.config.emulator, effectiveCore, original_rom, player_controllers, guns)
+                # change directory if wanted. it is restored on the way out: a rom on a
+                # squashfs is unmounted below, and a process sitting in a mount, even
+                # this one, keeps it busy
+                executionDirectory = generator.executionDirectory(system.config, rom)
+
                 with (
                     _evmapy_instance,
-                    set_hotkeygen_context(generator, system)
+                    set_hotkeygen_context(generator, system),
+                    contextlib.chdir(executionDirectory) if executionDirectory is not None
+                    else contextlib.nullcontext()
                 ):
-                    # change directory if wanted
-                    executionDirectory = generator.executionDirectory(system.config, rom)
-                    if executionDirectory is not None:
-                        os.chdir(executionDirectory)
-
                     # Initialize overlay process-tracking and check for active MangoHUD
                     bezel_proc = None
                     bezel_log_file = None

package/batocera/core/batocera-configgen/configgen/configgen/utils/overlayfs.py

@@ -9,6 +9,7 @@
 
 from ..batoceraPaths import mkdir_if_not_exists
 from ..exceptions import BatoceraException
+from .squashfs import unmount
 
 if TYPE_CHECKING:
     from collections.abc import Generator
@@ -19,15 +20,12 @@
 
 
 def _unmount_and_remove(mount_point: Path):
-    if mount_point.is_mount():
-        result = subprocess.run(["umount", str(mount_point)], capture_output=True, text=True)
-        if result.returncode != 0:
-            _logger.error("failed unmounting '%s' (rc=%d) because %s",
-                          mount_point, result.returncode, result.stderr.strip())
-
-            # Skip the follow-on removal if the umount failed because it might still
-            # be connected to the ROM's save area (system crashing or bad state?).
-            return
+    if mount_point.is_mount() and not unmount(mount_point):
+        _logger.error("failed unmounting '%s'", mount_point)
+
+        # Skip the follow-on removal if the umount failed because it might still
+        # be connected to the ROM's save area (system crashing or bad state?).
+        return
 
     shutil.rmtree(mount_point, ignore_errors=True)
 

package/batocera/core/batocera-configgen/configgen/configgen/utils/squashfs.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import contextlib
 import logging
 import subprocess
 from contextlib import contextmanager
@@ -17,6 +18,21 @@
 _SQUASHFS_DIR: Final = Path("/var/run/squashfs/")
 
 
+def unmount(mount_point: Path, /) -> bool:
+    result = subprocess.run(["umount", str(mount_point)], capture_output=True, text=True)
+
+    if result.returncode == 0:
+        return True
+
+    # a game that was killed rather than closed can leave a process holding the mount
+    # while it dies: detach it anyway, the kernel drops it once the last one lets go,
+    # leaving it mounted would keep the rom busy until the next reboot
+    _logger.warning("'%s' is busy, detaching it lazily because %s",
+                    mount_point, result.stderr.strip())
+
+    return subprocess.run(["umount", "-l", str(mount_point)], capture_output=True, text=True).returncode == 0
+
+
 @contextmanager
 def mount_squashfs(rom: Path, /) -> Generator[Path]:
     _logger.debug("mount_squashfs(%s)", rom)
@@ -27,14 +43,22 @@ def mount_squashfs(rom: Path, /) -> Generator[Path]:
     # first, try to clean an empty remaining directory (for example because of a crash)
     if mount_point.exists() and mount_point.is_dir():
         _logger.debug("squashfs_rom: %s already exists", mount_point)
-        # try to remove an empty directory, else, run the directory, ignoring the .squashfs
+
+        # a previous run may have left the rom mounted here, after a crash or an unmount
+        # that was refused: take it down rather than running the game off a stale mount,
+        # which isn't necessarily even the same rom
+        if mount_point.is_mount():
+            _logger.debug("squashfs_rom: %s is still mounted, unmounting it first", mount_point)
+            unmount(mount_point)
+
+        # whatever is left is not ours to run the game off: it isn't necessarily even
+        # the same rom, and it would never be unmounted either
         try:
             mount_point.rmdir()
-        except (FileNotFoundError, OSError):
-            _logger.debug("squashfs_rom: failed to rmdir %s", mount_point)
-            yield mount_point
-            # No cleanup is necessary
-            return
+        except FileNotFoundError:
+            pass
+        except OSError as e:
+            raise BatoceraException(f"Unable to clean the mount point {mount_point}") from e
 
     # ok, the base directory doesn't exist, let's create it and mount the squashfs on it
     mount_point.mkdir()
@@ -66,10 +90,10 @@ def mount_squashfs(rom: Path, /) -> Generator[Path]:
         _logger.debug("mount_squashfs: cleaning up %s", mount_point)
 
         # unmount
-        return_code = subprocess.call(["umount", mount_point])
-        if return_code != 0:
+        if not unmount(mount_point):
             _logger.debug("mount_squashfs: unmounting %s failed", mount_point)
             raise BatoceraException(f"Unable to unmount the file {mount_point}")
 
-        # cleaning the empty directory
-        mount_point.rmdir()
+        # cleaning the empty directory, a lazily detached mount may still hold it
+        with contextlib.suppress(OSError):
+            mount_point.rmdir()