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

Freeing an extent in XFS involves logging an EFI (extent free
intention), freeing the actual extent, and logging an EFD (extent
free done). The EFI object is created with a reference count of 2:
one for the current transaction and one for the subsequently created
EFD. Under normal circumstances, the first reference is dropped when
the EFI is unpinned and the second reference is dropped when the EFD
is committed to the on-disk log.

In event of errors or filesystem shutdown, there are various
potential cleanup scenarios depending on the state of the EFI/EFD.
The cleanup scenarios are confusing and racy, as demonstrated by the
following test sequence:

	# mount $dev $mnt
	# fsstress -d $mnt -n 99999 -p 16 -z -f fallocate=1 \
		-f punch=1 -f creat=1 -f unlink=1 &
	# sleep 5
	# killall -9 fsstress; wait
	# godown -f $mnt
	# umount

... in which the final umount can hang due to the AIL being pinned
indefinitely by one or more EFI items. This can occur due to several
conditions. For example, if the shutdown occurs after the EFI is
committed to the on-disk log and the EFD committed to the CIL, but
before the EFD committed to the log, the EFD iop_committed() abort
handler does not drop its reference to the EFI. Alternatively,
manual error injection in the xfs_bmap_finish() codepath shows that
if an error occurs after the EFI transaction is committed but before
the EFD is constructed and logged, the EFI is never released from
the AIL.

Update the EFI/EFD item handling code to use a more straightforward
and reliable approach to error handling. If an error occurs after
the EFI transaction is committed and before the EFD is constructed,
release the EFI explicitly from xfs_bmap_finish(). If the EFI
transaction is cancelled, release the EFI in the unlock handler.

Once the EFD is constructed, it is responsible for releasing the EFI
under any circumstances (including whether the EFI item aborts due
to log I/O error). Update the EFD item handlers to release the EFI
if the transaction is cancelled or aborts due to log I/O error.
Finally, update xfs_bmap_finish() to log at least one EFD extent to
the transaction before xfs_free_extent() errors are handled to
ensure the transaction is dirty and EFD item error handling is
triggered.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 49 insertions, 35 deletions

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 0f34886cf726..fa65f67737c5 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -67,16 +67,15 @@ xfs_fsb_to_db(struct xfs_inode *ip, xfs_fsblock_t fsb)
  */
 int						/* error */
 xfs_bmap_finish(
-	xfs_trans_t		**tp,		/* transaction pointer addr */
-	xfs_bmap_free_t		*flist,		/* i/o: list extents to free */
-	int			*committed)	/* xact committed or not */
+	struct xfs_trans		**tp,	/* transaction pointer addr */
+	struct xfs_bmap_free		*flist,	/* i/o: list extents to free */
+	int				*committed)/* xact committed or not */
 {
-	xfs_efd_log_item_t	*efd;		/* extent free data */
-	xfs_efi_log_item_t	*efi;		/* extent free intention */
-	int			error;		/* error return value */
-	xfs_bmap_free_item_t	*free;		/* free extent item */
-	xfs_mount_t		*mp;		/* filesystem mount structure */
-	xfs_bmap_free_item_t	*next;		/* next item on free list */
+	struct xfs_efd_log_item		*efd;	/* extent free data */
+	struct xfs_efi_log_item		*efi;	/* extent free intention */
+	int				error;	/* error return value */
+	struct xfs_bmap_free_item	*free;	/* free extent item */
+	struct xfs_bmap_free_item	*next;	/* next item on free list */
 
 	ASSERT((*tp)->t_flags & XFS_TRANS_PERM_LOG_RES);
 	if (flist->xbf_count == 0) {
@@ -88,40 +87,55 @@ xfs_bmap_finish(
 		xfs_trans_log_efi_extent(*tp, efi, free->xbfi_startblock,
 			free->xbfi_blockcount);
 
-	error = xfs_trans_roll(tp, NULL);
-	*committed = 1;
-	/*
-	 * We have a new transaction, so we should return committed=1,
-	 * even though we're returning an error.
-	 */
-	if (error)
+	error = __xfs_trans_roll(tp, NULL, committed);
+	if (error) {
+		/*
+		 * If the transaction was committed, drop the EFD reference
+		 * since we're bailing out of here. The other reference is
+		 * dropped when the EFI hits the AIL.
+		 *
+		 * If the transaction was not committed, the EFI is freed by the
+		 * EFI item unlock handler on abort. Also, we have a new
+		 * transaction so we should return committed=1 even though we're
+		 * returning an error.
+		 */
+		if (*committed) {
+			xfs_efi_release(efi);
+			xfs_force_shutdown((*tp)->t_mountp,
+				(error == -EFSCORRUPTED) ?
+					SHUTDOWN_CORRUPT_INCORE :
+					SHUTDOWN_META_IO_ERROR);
+		} else {
+			*committed = 1;
+		}
+
 		return error;
+	}
 
 	efd = xfs_trans_get_efd(*tp, efi, flist->xbf_count);
 	for (free = flist->xbf_first; free != NULL; free = next) {
 		next = free->xbfi_next;
-		if ((error = xfs_free_extent(*tp, free->xbfi_startblock,
-				free->xbfi_blockcount))) {
-			/*
-			 * The bmap free list will be cleaned up at a
-			 * higher level.  The EFI will be canceled when
-			 * this transaction is aborted.
-			 * Need to force shutdown here to make sure it
-			 * happens, since this transaction may not be
-			 * dirty yet.
-			 */
-			mp = (*tp)->t_mountp;
-			if (!XFS_FORCED_SHUTDOWN(mp))
-				xfs_force_shutdown(mp,
-						   (error == -EFSCORRUPTED) ?
-						   SHUTDOWN_CORRUPT_INCORE :
-						   SHUTDOWN_META_IO_ERROR);
-			return error;
-		}
+
+		/*
+		 * Free the extent and log the EFD to dirty the transaction
+		 * before handling errors. This ensures that the transaction is
+		 * aborted, which:
+		 *
+		 * 1.) releases the EFI and frees the EFD
+		 * 2.) shuts down the filesystem
+		 *
+		 * The bmap free list is cleaned up at a higher level.
+		 */
+		error = xfs_free_extent(*tp, free->xbfi_startblock,
+					free->xbfi_blockcount);
 		xfs_trans_log_efd_extent(*tp, efd, free->xbfi_startblock,
-			free->xbfi_blockcount);
+					 free->xbfi_blockcount);
+		if (error)
+			return error;
+
 		xfs_bmap_del_free(flist, NULL, free);
 	}
+
 	return 0;
 }