fix(csi-node): cherry-pick remount staging path as ro before final um…

…ount

Sometimes after/during disconnect we get some page write errors, triggered by a journal update by
the JBD2 worker task.
We don't really know how we can "flush" these tasks so at the moment the best solution we have is
to remount the staging path as RO before we umount it for good, which seems to help.

Signed-off-by: Tiago Castro <[email protected]>

csi/src/filesystem_vol.rs

@@ -55,15 +55,24 @@ pub async fn stage_fs_volume(
         }
     };
 
-    if mount::find_mount(Some(&device_path), Some(fs_staging_path)).is_some() {
+    if let Some(existing) =
+        mount::find_mount(Some(&device_path), Some(fs_staging_path))
+    {
         debug!(
             "Device {} is already mounted onto {}",
             device_path, fs_staging_path
         );
+
         info!(
-            "Volume {} is already staged to {}",
-            volume_id, fs_staging_path
+            %existing,
+            "Volume {} is already staged to {}", volume_id, fs_staging_path
         );
+
+        // todo: validate other flags?
+        if mnt.mount_flags.readonly() != existing.options.readonly() {
+            mount::remount(fs_staging_path, mnt.mount_flags.readonly())?;
+        }
+
         return Ok(());
     }
 
@@ -152,6 +161,14 @@ pub async fn unstage_fs_volume(
                 unkown_mount.source
             ));
         }
+
+        // Sometimes after/during disconnect we get some page write errors,
+        // triggered by a journal update by the JBD2 worker task. We
+        // don't really know how we can "flush" these tasks so at the
+        // moment the best solution we have is to remount the staging path
+        // as RO before we umount it for good, which seems to help.
+        mount::remount(fs_staging_path, true)?;
+
         if let Err(error) = mount::filesystem_unmount(fs_staging_path) {
             return Err(failure!(
                 Code::Internal,

csi/src/mount.rs

@@ -262,6 +262,23 @@ pub fn bind_unmount(target: &str) -> Result<(), Error> {
     Ok(())
 }
 
+/// Remount existing mount as read only or read write.
+pub(crate) fn remount(target: &str, ro: bool) -> Result<Mount, Error> {
+    let mut flags = MountFlags::empty();
+    flags.insert(MountFlags::REMOUNT);
+
+    if ro {
+        flags.insert(MountFlags::RDONLY);
+    }
+
+    let mount =
+        Mount::new("", target, FilesystemType::Manual("none"), flags, None)?;
+
+    debug!("Target {} remounted with {:?}", target, flags);
+
+    Ok(mount)
+}
+
 /// Mount a block device
 pub fn blockdevice_mount(
     source: &str,