xfs: fix efi/efd error handling to avoid fs shutdown hangs

[linux-2.6-microblaze.git] / fs / xfs / xfs_extfree_item.h

diff --git a/fs/xfs/xfs_extfree_item.h b/fs/xfs/xfs_extfree_item.h
index 399562e..8fa8651 100644 (file)
--- a/fs/xfs/xfs_extfree_item.h
+++ b/fs/xfs/xfs_extfree_item.h
@@ -39,9 +39,28 @@ struct kmem_zone;
  * "extent free done" log item described below.
  *
  * The EFI is reference counted so that it is not freed prior to both the EFI
- * and EFD being committed and unpinned. This ensures that when the last
- * reference goes away the EFI will always be in the AIL as it has been
- * unpinned, regardless of whether the EFD is processed before or after the EFI.
+ * and EFD being committed and unpinned. This ensures the EFI is inserted into
+ * the AIL even in the event of out of order EFI/EFD processing. In other words,
+ * an EFI is born with two references:
+ *
+ *     1.) an EFI held reference to track EFI AIL insertion
+ *     2.) an EFD held reference to track EFD commit
+ *
+ * On allocation, both references are the responsibility of the caller. Once the
+ * EFI is added to and dirtied in a transaction, ownership of reference one
+ * transfers to the transaction. The reference is dropped once the EFI is
+ * inserted to the AIL or in the event of failure along the way (e.g., commit
+ * failure, log I/O error, etc.). Note that the caller remains responsible for
+ * the EFD reference under all circumstances to this point. The caller has no
+ * means to detect failure once the transaction is committed, however.
+ * Therefore, an EFD is required after this point, even in the event of
+ * unrelated failure.
+ *
+ * Once an EFD is allocated and dirtied in a transaction, reference two
+ * transfers to the transaction. The EFD reference is dropped once it reaches
+ * the unpin handler. Similar to the EFI, the reference also drops in the event
+ * of commit failure or log I/O errors. Note that the EFD is not inserted in the
+ * AIL, so at this point both the EFI and EFD are freed.
  */
 typedef struct xfs_efi_log_item {
        xfs_log_item_t          efi_item;