4 files changed, 218 insertions, 109 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 0b02c64..4184085 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -900,7 +900,7 @@ xfs_log_move_tail(xfs_mount_t	*mp,
 int
 xfs_log_need_covered(xfs_mount_t *mp)
 {
-	int		needed = 0, gen;
+	int		needed = 0;
 	xlog_t		*log = mp->m_log;
 
 	if (!xfs_fs_writable(mp))
@@ -909,7 +909,7 @@ xfs_log_need_covered(xfs_mount_t *mp)
 	spin_lock(&log->l_icloglock);
 	if (((log->l_covered_state == XLOG_STATE_COVER_NEED) ||
 		(log->l_covered_state == XLOG_STATE_COVER_NEED2))
-			&& !xfs_trans_first_ail(mp, &gen)
+			&& !xfs_trans_first_ail(mp, NULL)
 			&& xlog_iclogs_empty(log)) {
 		if (log->l_covered_state == XLOG_STATE_COVER_NEED)
 			log->l_covered_state = XLOG_STATE_COVER_DONE;
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 199c8ea..37ba489 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -54,10 +54,8 @@ STATIC void	xlog_recover_insert_item_backq(xlog_recover_item_t **q,
 					       xlog_recover_item_t *item);
 #if defined(DEBUG)
 STATIC void	xlog_recover_check_summary(xlog_t *);
-STATIC void	xlog_recover_check_ail(xfs_mount_t *, xfs_log_item_t *, int);
 #else
 #define	xlog_recover_check_summary(log)
-#define	xlog_recover_check_ail(mp, lip, gen)
 #endif
 
 
@@ -2710,8 +2708,8 @@ xlog_recover_do_efd_trans(
 	xfs_efd_log_format_t	*efd_formatp;
 	xfs_efi_log_item_t	*efip = NULL;
 	xfs_log_item_t		*lip;
-	int			gen;
 	__uint64_t		efi_id;
+	struct xfs_ail_cursor	cur;
 
 	if (pass == XLOG_RECOVER_PASS1) {
 		return;
@@ -2730,7 +2728,8 @@ xlog_recover_do_efd_trans(
 	 */
 	mp = log->l_mp;
 	spin_lock(&mp->m_ail_lock);
-	lip = xfs_trans_first_ail(mp, &gen);
+	xfs_trans_ail_cursor_init(mp->m_ail, &cur);
+	lip = xfs_trans_first_ail(mp, &cur);
 	while (lip != NULL) {
 		if (lip->li_type == XFS_LI_EFI) {
 			efip = (xfs_efi_log_item_t *)lip;
@@ -2741,11 +2740,13 @@ xlog_recover_do_efd_trans(
 				 */
 				xfs_trans_delete_ail(mp, lip);
 				xfs_efi_item_free(efip);
-				return;
+				spin_lock(&mp->m_ail_lock);
+				break;
 			}
 		}
-		lip = xfs_trans_next_ail(mp, lip, &gen, NULL);
+		lip = xfs_trans_next_ail(mp, &cur);
 	}
+	xfs_trans_ail_cursor_done(mp->m_ail, &cur);
 	spin_unlock(&mp->m_ail_lock);
 }
 
@@ -3030,33 +3031,6 @@ abort_error:
 }
 
 /*
- * Verify that once we've encountered something other than an EFI
- * in the AIL that there are no more EFIs in the AIL.
- */
-#if defined(DEBUG)
-STATIC void
-xlog_recover_check_ail(
-	xfs_mount_t		*mp,
-	xfs_log_item_t		*lip,
-	int			gen)
-{
-	int			orig_gen = gen;
-
-	do {
-		ASSERT(lip->li_type != XFS_LI_EFI);
-		lip = xfs_trans_next_ail(mp, lip, &gen, NULL);
-		/*
-		 * The check will be bogus if we restart from the
-		 * beginning of the AIL, so ASSERT that we don't.
-		 * We never should since we're holding the AIL lock
-		 * the entire time.
-		 */
-		ASSERT(gen == orig_gen);
-	} while (lip != NULL);
-}
-#endif	/* DEBUG */
-
-/*
  * When this is called, all of the EFIs which did not have
  * corresponding EFDs should be in the AIL.  What we do now
  * is free the extents associated with each one.
@@ -3080,20 +3054,25 @@ xlog_recover_process_efis(
 {
 	xfs_log_item_t		*lip;
 	xfs_efi_log_item_t	*efip;
-	int			gen;
 	xfs_mount_t		*mp;
 	int			error = 0;
+	struct xfs_ail_cursor	cur;
 
 	mp = log->l_mp;
 	spin_lock(&mp->m_ail_lock);
 
-	lip = xfs_trans_first_ail(mp, &gen);
+	xfs_trans_ail_cursor_init(mp->m_ail, &cur);
+	lip = xfs_trans_first_ail(mp, &cur);
 	while (lip != NULL) {
 		/*
 		 * We're done when we see something other than an EFI.
+		 * There should be no EFIs left in the AIL now.
 		 */
 		if (lip->li_type != XFS_LI_EFI) {
-			xlog_recover_check_ail(mp, lip, gen);
+#ifdef DEBUG
+			for (; lip; lip = xfs_trans_next_ail(mp, &cur))
+				ASSERT(lip->li_type != XFS_LI_EFI);
+#endif
 			break;
 		}
 
@@ -3102,17 +3081,19 @@ xlog_recover_process_efis(
 		 */
 		efip = (xfs_efi_log_item_t *)lip;
 		if (efip->efi_flags & XFS_EFI_RECOVERED) {
-			lip = xfs_trans_next_ail(mp, lip, &gen, NULL);
+			lip = xfs_trans_next_ail(mp, &cur);
 			continue;
 		}
 
 		spin_unlock(&mp->m_ail_lock);
 		error = xlog_recover_process_efi(mp, efip);
-		if (error)
-			return error;
 		spin_lock(&mp->m_ail_lock);
-		lip = xfs_trans_next_ail(mp, lip, &gen, NULL);
+		if (error)
+			goto out;
+		lip = xfs_trans_next_ail(mp, &cur);
 	}
+out:
+	xfs_trans_ail_cursor_done(mp->m_ail, &cur);
 	spin_unlock(&mp->m_ail_lock);
 	return error;
 }
diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index db72b52..7b8bfcf 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -99,26 +99,137 @@ xfs_trans_push_ail(
 }
 
 /*
+ * AIL traversal cursor initialisation.
+ *
+ * The cursor keeps track of where our current traversal is up
+ * to by tracking the next ƣtem in the list for us. However, for
+ * this to be safe, removing an object from the AIL needs to invalidate
+ * any cursor that points to it. hence the traversal cursor needs to
+ * be linked to the struct xfs_ail so that deletion can search all the
+ * active cursors for invalidation.
+ *
+ * We don't link the push cursor because it is embedded in the struct
+ * xfs_ail and hence easily findable.
+ */
+void
+xfs_trans_ail_cursor_init(
+	struct xfs_ail		*ailp,
+	struct xfs_ail_cursor	*cur)
+{
+	cur->item = NULL;
+	if (cur == &ailp->xa_cursors)
+		return;
+
+	cur->next = ailp->xa_cursors.next;
+	ailp->xa_cursors.next = cur;
+}
+
+/*
+ * Set the cursor to the next item, because when we look
+ * up the cursor the current item may have been freed.
+ */
+STATIC void
+xfs_trans_ail_cursor_set(
+	struct xfs_ail		*ailp,
+	struct xfs_ail_cursor	*cur,
+	struct xfs_log_item	*lip)
+{
+	if (lip)
+		cur->item = xfs_ail_next(ailp, lip);
+}
+
+/*
+ * Get the next item in the traversal and advance the cursor.
+ * If the cursor was invalidated (inidicated by a lip of 1),
+ * restart the traversal.
+ */
+STATIC struct xfs_log_item *
+xfs_trans_ail_cursor_next(
+	struct xfs_ail		*ailp,
+	struct xfs_ail_cursor	*cur)
+{
+	struct xfs_log_item	*lip = cur->item;
+
+	if ((__psint_t)lip & 1)
+		lip = xfs_ail_min(ailp);
+	xfs_trans_ail_cursor_set(ailp, cur, lip);
+	return lip;
+}
+
+/*
+ * Invalidate any cursor that is pointing to this item. This is
+ * called when an item is removed from the AIL. Any cursor pointing
+ * to this object is now invalid and the traversal needs to be
+ * terminated so it doesn't reference a freed object. We set the
+ * cursor item to a value of 1 so we can distinguish between an
+ * invalidation and the end of the list when getting the next item
+ * from the cursor.
+ */
+STATIC void
+xfs_trans_ail_cursor_clear(
+	struct xfs_ail		*ailp,
+	struct xfs_log_item	*lip)
+{
+	struct xfs_ail_cursor	*cur;
+
+	/* need to search all cursors */
+	for (cur = &ailp->xa_cursors; cur; cur = cur->next) {
+		if (cur->item == lip)
+			cur->item = (struct xfs_log_item *)
+					((__psint_t)cur->item | 1);
+	}
+}
+
+/*
+ * Now that the traversal is complete, we need to remove the cursor
+ * from the list of traversing cursors. Avoid removing the embedded
+ * push cursor, but use the fact it is alway present to make the
+ * list deletion simple.
+ */
+void
+xfs_trans_ail_cursor_done(
+	struct xfs_ail		*ailp,
+	struct xfs_ail_cursor	*done)
+{
+	struct xfs_ail_cursor	*prev = NULL;
+	struct xfs_ail_cursor	*cur;
+
+	done->item = NULL;
+	if (done == &ailp->xa_cursors)
+		return;
+	prev = &ailp->xa_cursors;
+	for (cur = prev->next; cur; prev = cur, cur = prev->next) {
+		if (cur == done) {
+			prev->next = cur->next;
+			break;
+		}
+	}
+	ASSERT(cur);
+}
+
+/*
  * Return the item in the AIL with the current lsn.
  * Return the current tree generation number for use
  * in calls to xfs_trans_next_ail().
  */
 STATIC xfs_log_item_t *
 xfs_trans_first_push_ail(
-	xfs_mount_t	*mp,
-	int		*gen,
-	xfs_lsn_t	lsn)
+	struct xfs_ail		*ailp,
+	struct xfs_ail_cursor	*cur,
+	xfs_lsn_t		lsn)
 {
-	xfs_log_item_t	*lip;
+	xfs_log_item_t		*lip;
 
-	lip = xfs_ail_min(mp->m_ail);
-	*gen = (int)mp->m_ail->xa_gen;
+	lip = xfs_ail_min(ailp);
+	xfs_trans_ail_cursor_set(ailp, cur, lip);
 	if (lsn == 0)
 		return lip;
 
-	list_for_each_entry(lip, &mp->m_ail->xa_ail, li_ail) {
-		if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0)
+	list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
+		if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0) {
+			xfs_trans_ail_cursor_set(ailp, cur, lip);
 			return lip;
+		}
 	}
 
 	return NULL;
@@ -137,22 +248,21 @@ xfsaild_push(
 	xfs_lsn_t	target =  ailp->xa_target;
 	xfs_lsn_t	lsn;
 	xfs_log_item_t	*lip;
-	int		gen;
-	int		restarts;
 	int		flush_log, count, stuck;
 	xfs_mount_t	*mp = ailp->xa_mount;
-
-#define	XFS_TRANS_PUSH_AIL_RESTARTS	10
+	struct xfs_ail_cursor	*cur = &ailp->xa_cursors;
 
 	spin_lock(&mp->m_ail_lock);
-	lip = xfs_trans_first_push_ail(mp, &gen, *last_lsn);
+	xfs_trans_ail_cursor_init(ailp, cur);
+	lip = xfs_trans_first_push_ail(ailp, cur, *last_lsn);
 	if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
 		/*
 		 * AIL is empty or our push has reached the end.
 		 */
+		xfs_trans_ail_cursor_done(ailp, cur);
 		spin_unlock(&mp->m_ail_lock);
 		last_pushed_lsn = 0;
-		goto out;
+		return tout;
 	}
 
 	XFS_STATS_INC(xs_push_ail);
@@ -170,7 +280,7 @@ xfsaild_push(
 	 */
 	tout = 10;
 	lsn = lip->li_lsn;
-	flush_log = stuck = count = restarts = 0;
+	flush_log = stuck = count = 0;
 	while ((XFS_LSN_CMP(lip->li_lsn, target) < 0)) {
 		int	lock_result;
 		/*
@@ -245,13 +355,12 @@ xfsaild_push(
 		if (stuck > 100)
 			break;
 
-		lip = xfs_trans_next_ail(mp, lip, &gen, &restarts);
+		lip = xfs_trans_ail_cursor_next(ailp, cur);
 		if (lip == NULL)
 			break;
-		if (restarts > XFS_TRANS_PUSH_AIL_RESTARTS)
-			break;
 		lsn = lip->li_lsn;
 	}
+	xfs_trans_ail_cursor_done(ailp, cur);
 	spin_unlock(&mp->m_ail_lock);
 
 	if (flush_log) {
@@ -275,8 +384,7 @@ xfsaild_push(
 		 */
 		tout += 20;
 		last_pushed_lsn = 0;
-	} else if ((restarts > XFS_TRANS_PUSH_AIL_RESTARTS) ||
-		   ((stuck * 100) / count > 90)) {
+	} else if ((stuck * 100) / count > 90) {
 		/*
 		 * Either there is a lot of contention on the AIL or we
 		 * are stuck due to operations in progress. "Stuck" in this
@@ -288,7 +396,6 @@ xfsaild_push(
 		 */
 		tout += 10;
 	}
-out:
 	*last_lsn = last_pushed_lsn;
 	return tout;
 }	/* xfsaild_push */
@@ -348,9 +455,6 @@ xfs_trans_unlocked_item(
  * we move in the AIL is the minimum one, update the tail lsn in the
  * log manager.
  *
- * Increment the AIL's generation count to indicate that the tree
- * has changed.
- *
  * This function must be called with the AIL lock held.  The lock
  * is dropped before returning.
  */
@@ -368,14 +472,13 @@ xfs_trans_update_ail(
 	if (lip->li_flags & XFS_LI_IN_AIL) {
 		dlip = xfs_ail_delete(mp->m_ail, lip);
 		ASSERT(dlip == lip);
+		xfs_trans_ail_cursor_clear(mp->m_ail, dlip);
 	} else {
 		lip->li_flags |= XFS_LI_IN_AIL;
 	}
 
 	lip->li_lsn = lsn;
-
 	xfs_ail_insert(mp->m_ail, lip);
-	mp->m_ail->xa_gen++;
 
 	if (mlip == dlip) {
 		mlip = xfs_ail_min(mp->m_ail);
@@ -415,11 +518,11 @@ xfs_trans_delete_ail(
 		mlip = xfs_ail_min(mp->m_ail);
 		dlip = xfs_ail_delete(mp->m_ail, lip);
 		ASSERT(dlip == lip);
+		xfs_trans_ail_cursor_clear(mp->m_ail, dlip);
 
 
 		lip->li_flags &= ~XFS_LI_IN_AIL;
 		lip->li_lsn = 0;
-		mp->m_ail->xa_gen++;
 
 		if (mlip == dlip) {
 			mlip = xfs_ail_min(mp->m_ail);
@@ -455,46 +558,29 @@ xfs_trans_delete_ail(
  */
 xfs_log_item_t *
 xfs_trans_first_ail(
-	xfs_mount_t	*mp,
-	int		*gen)
+	struct xfs_mount	*mp,
+	struct xfs_ail_cursor	*cur)
 {
-	xfs_log_item_t	*lip;
+	xfs_log_item_t		*lip;
+	struct xfs_ail		*ailp = mp->m_ail;
 
-	lip = xfs_ail_min(mp->m_ail);
-	*gen = (int)mp->m_ail->xa_gen;
+	lip = xfs_ail_min(ailp);
+	xfs_trans_ail_cursor_set(ailp, cur, lip);
 
 	return lip;
 }
 
 /*
- * If the generation count of the tree has not changed since the
- * caller last took something from the AIL, then return the elmt
- * in the tree which follows the one given.  If the count has changed,
- * then return the minimum elmt of the AIL and bump the restarts counter
- * if one is given.
+ * Grab the next item in the AIL from the cursor passed in.
  */
 xfs_log_item_t *
 xfs_trans_next_ail(
-	xfs_mount_t	*mp,
-	xfs_log_item_t	*lip,
-	int		*gen,
-	int		*restarts)
+	struct xfs_mount	*mp,
+	struct xfs_ail_cursor	*cur)
 {
-	xfs_log_item_t	*nlip;
-
-	ASSERT(mp && lip && gen);
-	if (mp->m_ail->xa_gen == *gen) {
-		nlip = xfs_ail_next(mp->m_ail, lip);
-	} else {
-		nlip = xfs_ail_min(mp->m_ail);
-		*gen = (int)mp->m_ail->xa_gen;
-		if (restarts != NULL) {
-			XFS_STATS_INC(xs_push_ail_restarts);
-			(*restarts)++;
-		}
-	}
+	struct xfs_ail		*ailp = mp->m_ail;
 
-	return (nlip);
+	return xfs_trans_ail_cursor_next(ailp, cur);
 }
 
 
@@ -517,6 +603,7 @@ xfs_trans_ail_init(
 	xfs_mount_t	*mp)
 {
 	struct xfs_ail	*ailp;
+	int		error;
 
 	ailp = kmem_zalloc(sizeof(struct xfs_ail), KM_MAYFAIL);
 	if (!ailp)
@@ -524,7 +611,15 @@ xfs_trans_ail_init(
 
 	ailp->xa_mount = mp;
 	INIT_LIST_HEAD(&ailp->xa_ail);
-	return xfsaild_start(ailp);
+	error = xfsaild_start(ailp);
+	if (error)
+		goto out_free_ailp;
+	mp->m_ail = ailp;
+	return 0;
+
+out_free_ailp:
+	kmem_free(ailp);
+	return error;
 }
 
 void
diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h
index 98317fd..f114d38 100644
--- a/fs/xfs/xfs_trans_priv.h
+++ b/fs/xfs/xfs_trans_priv.h
@@ -44,20 +44,33 @@ xfs_log_busy_slot_t		*xfs_trans_add_busy(xfs_trans_t *tp,
 						    xfs_extlen_t idx);
 
 /*
- * From xfs_trans_ail.c
+ * AIL traversal cursor.
+ *
+ * Rather than using a generation number for detecting changes in the ail, use
+ * a cursor that is protected by the ail lock. The aild cursor exists in the
+ * struct xfs_ail, but other traversals can declare it on the stack and link it
+ * to the ail list.
+ *
+ * When an object is deleted from or moved int the AIL, the cursor list is
+ * searched to see if the object is a designated cursor item. If it is, it is
+ * deleted from the cursor so that the next time the cursor is used traversal
+ * will return to the start.
+ *
+ * This means a traversal colliding with a removal will cause a restart of the
+ * list scan, rather than any insertion or deletion anywhere in the list. The
+ * low bit of the item pointer is set if the cursor has been invalidated so
+ * that we can tell the difference between invalidation and reaching the end
+ * of the list to trigger traversal restarts.
  */
-void			xfs_trans_update_ail(struct xfs_mount *mp,
-				     struct xfs_log_item *lip, xfs_lsn_t lsn)
-				     __releases(mp->m_ail_lock);
-void			xfs_trans_delete_ail(struct xfs_mount *mp,
-				     struct xfs_log_item *lip)
-				     __releases(mp->m_ail_lock);
-struct xfs_log_item	*xfs_trans_first_ail(struct xfs_mount *, int *);
-struct xfs_log_item	*xfs_trans_next_ail(struct xfs_mount *,
-				     struct xfs_log_item *, int *, int *);
+struct xfs_ail_cursor {
+	struct xfs_ail_cursor	*next;
+	struct xfs_log_item	*item;
+};
 
 /*
- * AIL push thread support
+ * Private AIL structures.
+ *
+ * Eventually we need to drive the locking in here as well.
  */
 struct xfs_ail {
 	struct xfs_mount	*xa_mount;
@@ -65,8 +78,28 @@ struct xfs_ail {
 	uint			xa_gen;
 	struct task_struct	*xa_task;
 	xfs_lsn_t		xa_target;
+	struct xfs_ail_cursor	xa_cursors;
 };
 
+/*
+ * From xfs_trans_ail.c
+ */
+void			xfs_trans_update_ail(struct xfs_mount *mp,
+				     struct xfs_log_item *lip, xfs_lsn_t lsn)
+				     __releases(mp->m_ail_lock);
+void			xfs_trans_delete_ail(struct xfs_mount *mp,
+				     struct xfs_log_item *lip)
+				     __releases(mp->m_ail_lock);
+struct xfs_log_item	*xfs_trans_first_ail(struct xfs_mount *mp,
+					struct xfs_ail_cursor *cur);
+struct xfs_log_item	*xfs_trans_next_ail(struct xfs_mount *mp,
+					struct xfs_ail_cursor *cur);
+
+void xfs_trans_ail_cursor_init(struct xfs_ail *ailp,
+					struct xfs_ail_cursor *cur);
+void xfs_trans_ail_cursor_done(struct xfs_ail *ailp,
+					struct xfs_ail_cursor *cur);
+
 long	xfsaild_push(struct xfs_ail *, xfs_lsn_t *);
 void	xfsaild_wakeup(struct xfs_ail *, xfs_lsn_t);
 int	xfsaild_start(struct xfs_ail *);