[PATCH 16/67] xfs: allow pausing of pending deferred work items

[cem@kernel.org]

From: "Darrick J. Wong" <djwong@kernel.org>

Source kernel commit: 4dffb2cbb4839fd6f9bbac0b3fd06cc9015cbb9b

Traditionally, all pending deferred work attached to a transaction is
finished when one of the xfs_defer_finish* functions is called.
However, online repair wants to be able to allocate space for a new data
structure, format a new metadata structure into the allocated space, and

As a hedge against system crashes during repairs, we also want to log
some EFI items for the allocated space speculatively, and cancel them if
we elect to commit the new data structure.

Therefore, introduce the idea of pausing a pending deferred work item.
Log intent items are still created for paused items and relogged as
necessary.  However, paused items are pushed onto a side list before we
start calling ->finish_item, and the whole list is reattach to the
transaction afterwards.  New work items are never attached to paused
pending items.

Modify xfs_defer_cancel to clean up pending deferred work items holding
a log intent item but not a log intent done item, since that is now
possible.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
---
 include/list.h      |  6 +++
 include/xfs_trace.h |  3 ++
 libxfs/xfs_defer.c  | 97 +++++++++++++++++++++++++++++++++++++++------
 libxfs/xfs_defer.h  | 17 +++++++-
 4 files changed, 109 insertions(+), 14 deletions(-)

diff --git a/include/list.h b/include/list.h
index e59cbd537..52b53c7a3 100644
--- a/include/list.h
+++ b/include/list.h
@@ -152,6 +152,12 @@ static inline void list_splice_init(struct list_head *list,
 #define list_first_entry(ptr, type, member) \
 	list_entry((ptr)->next, type, member)
 
+#define list_first_entry_or_null(ptr, type, member) ({ \
+	struct list_head *head__ = (ptr); \
+	struct list_head *pos__ = READ_ONCE(head__->next); \
+	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
+})
+
 #define container_of(ptr, type, member) ({			\
 	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
 	(type *)( (char *)__mptr - offsetof(type,member) );})
diff --git a/include/xfs_trace.h b/include/xfs_trace.h
index c79a4bd74..06d6aa950 100644
--- a/include/xfs_trace.h
+++ b/include/xfs_trace.h
@@ -337,5 +337,8 @@
 #define trace_xfs_fs_mark_healthy(a,b)		((void) 0)
 
 #define trace_xlog_intent_recovery_failed(...)	((void) 0)
+#define trace_xfs_defer_isolate_paused(...)	((void) 0)
+#define trace_xfs_defer_item_pause(...)		((void) 0)
+#define trace_xfs_defer_item_unpause(...)	((void) 0)
 
 #endif /* __TRACE_H__ */
diff --git a/libxfs/xfs_defer.c b/libxfs/xfs_defer.c
index 200d1b300..58ad1881d 100644
--- a/libxfs/xfs_defer.c
+++ b/libxfs/xfs_defer.c
@@ -481,7 +481,7 @@ xfs_defer_relog_intent(
  * done item to release the intent item; and then log a new intent item.
  * The caller should provide a fresh transaction and roll it after we're done.
  */
-static int
+static void
 xfs_defer_relog(
 	struct xfs_trans		**tpp,
 	struct list_head		*dfops)
@@ -523,10 +523,6 @@ xfs_defer_relog(
 
 		xfs_defer_relog_intent(*tpp, dfp);
 	}
-
-	if ((*tpp)->t_flags & XFS_TRANS_DIRTY)
-		return xfs_defer_trans_roll(tpp);
-	return 0;
 }
 
 /*
@@ -582,6 +578,24 @@ out:
 	return error;
 }
 
+/* Move all paused deferred work from @tp to @paused_list. */
+static void
+xfs_defer_isolate_paused(
+	struct xfs_trans		*tp,
+	struct list_head		*paused_list)
+{
+	struct xfs_defer_pending	*dfp;
+	struct xfs_defer_pending	*pli;
+
+	list_for_each_entry_safe(dfp, pli, &tp->t_dfops, dfp_list) {
+		if (!(dfp->dfp_flags & XFS_DEFER_PAUSED))
+			continue;
+
+		list_move_tail(&dfp->dfp_list, paused_list);
+		trace_xfs_defer_isolate_paused(tp->t_mountp, dfp);
+	}
+}
+
 /*
  * Finish all the pending work.  This involves logging intent items for
  * any work items that wandered in since the last transaction roll (if
@@ -597,6 +611,7 @@ xfs_defer_finish_noroll(
 	struct xfs_defer_pending	*dfp = NULL;
 	int				error = 0;
 	LIST_HEAD(dop_pending);
+	LIST_HEAD(dop_paused);
 
 	ASSERT((*tp)->t_flags & XFS_TRANS_PERM_LOG_RES);
 
@@ -615,6 +630,8 @@ xfs_defer_finish_noroll(
 		 */
 		int has_intents = xfs_defer_create_intents(*tp);
 
+		xfs_defer_isolate_paused(*tp, &dop_paused);
+
 		list_splice_init(&(*tp)->t_dfops, &dop_pending);
 
 		if (has_intents < 0) {
@@ -627,22 +644,33 @@ xfs_defer_finish_noroll(
 				goto out_shutdown;
 
 			/* Relog intent items to keep the log moving. */
-			error = xfs_defer_relog(tp, &dop_pending);
-			if (error)
-				goto out_shutdown;
+			xfs_defer_relog(tp, &dop_pending);
+			xfs_defer_relog(tp, &dop_paused);
+
+			if ((*tp)->t_flags & XFS_TRANS_DIRTY) {
+				error = xfs_defer_trans_roll(tp);
+				if (error)
+					goto out_shutdown;
+			}
 		}
 
-		dfp = list_first_entry(&dop_pending, struct xfs_defer_pending,
-				       dfp_list);
+		dfp = list_first_entry_or_null(&dop_pending,
+				struct xfs_defer_pending, dfp_list);
+		if (!dfp)
+			break;
 		error = xfs_defer_finish_one(*tp, dfp);
 		if (error && error != -EAGAIN)
 			goto out_shutdown;
 	}
 
+	/* Requeue the paused items in the outgoing transaction. */
+	list_splice_tail_init(&dop_paused, &(*tp)->t_dfops);
+
 	trace_xfs_defer_finish_done(*tp, _RET_IP_);
 	return 0;
 
 out_shutdown:
+	list_splice_tail_init(&dop_paused, &dop_pending);
 	xfs_defer_trans_abort(*tp, &dop_pending);
 	xfs_force_shutdown((*tp)->t_mountp, SHUTDOWN_CORRUPT_INCORE);
 	trace_xfs_defer_finish_error(*tp, error);
@@ -655,6 +683,9 @@ int
 xfs_defer_finish(
 	struct xfs_trans	**tp)
 {
+#ifdef DEBUG
+	struct xfs_defer_pending *dfp;
+#endif
 	int			error;
 
 	/*
@@ -674,7 +705,10 @@ xfs_defer_finish(
 	}
 
 	/* Reset LOWMODE now that we've finished all the dfops. */
-	ASSERT(list_empty(&(*tp)->t_dfops));
+#ifdef DEBUG
+	list_for_each_entry(dfp, &(*tp)->t_dfops, dfp_list)
+		ASSERT(dfp->dfp_flags & XFS_DEFER_PAUSED);
+#endif
 	(*tp)->t_flags &= ~XFS_TRANS_LOWMODE;
 	return 0;
 }
@@ -686,6 +720,7 @@ xfs_defer_cancel(
 	struct xfs_mount	*mp = tp->t_mountp;
 
 	trace_xfs_defer_cancel(tp, _RET_IP_);
+	xfs_defer_trans_abort(tp, &tp->t_dfops);
 	xfs_defer_cancel_list(mp, &tp->t_dfops);
 }
 
@@ -727,6 +762,10 @@ xfs_defer_can_append(
 	if (dfp->dfp_intent)
 		return false;
 
+	/* Paused items cannot absorb more work */
+	if (dfp->dfp_flags & XFS_DEFER_PAUSED)
+		return NULL;
+
 	/* Already full? */
 	if (ops->max_items && dfp->dfp_count >= ops->max_items)
 		return false;
@@ -735,7 +774,7 @@ xfs_defer_can_append(
 }
 
 /* Add an item for later deferred processing. */
-void
+struct xfs_defer_pending *
 xfs_defer_add(
 	struct xfs_trans		*tp,
 	enum xfs_defer_ops_type		type,
@@ -762,6 +801,7 @@ xfs_defer_add(
 
 	xfs_defer_add_item(dfp, li);
 	trace_xfs_defer_add_item(tp->t_mountp, dfp, li);
+	return dfp;
 }
 
 /*
@@ -1087,3 +1127,36 @@ xfs_defer_destroy_item_caches(void)
 	xfs_rmap_intent_destroy_cache();
 	xfs_defer_destroy_cache();
 }
+
+/*
+ * Mark a deferred work item so that it will be requeued indefinitely without
+ * being finished.  Caller must ensure there are no data dependencies on this
+ * work item in the meantime.
+ */
+void
+xfs_defer_item_pause(
+	struct xfs_trans		*tp,
+	struct xfs_defer_pending	*dfp)
+{
+	ASSERT(!(dfp->dfp_flags & XFS_DEFER_PAUSED));
+
+	dfp->dfp_flags |= XFS_DEFER_PAUSED;
+
+	trace_xfs_defer_item_pause(tp->t_mountp, dfp);
+}
+
+/*
+ * Release a paused deferred work item so that it will be finished during the
+ * next transaction roll.
+ */
+void
+xfs_defer_item_unpause(
+	struct xfs_trans		*tp,
+	struct xfs_defer_pending	*dfp)
+{
+	ASSERT(dfp->dfp_flags & XFS_DEFER_PAUSED);
+
+	dfp->dfp_flags &= ~XFS_DEFER_PAUSED;
+
+	trace_xfs_defer_item_unpause(tp->t_mountp, dfp);
+}
diff --git a/libxfs/xfs_defer.h b/libxfs/xfs_defer.h
index 78d6dcd1a..b0284154f 100644
--- a/libxfs/xfs_defer.h
+++ b/libxfs/xfs_defer.h
@@ -34,11 +34,24 @@ struct xfs_defer_pending {
 	struct xfs_log_item		*dfp_intent;	/* log intent item */
 	struct xfs_log_item		*dfp_done;	/* log done item */
 	unsigned int			dfp_count;	/* # extent items */
+	unsigned int			dfp_flags;
 	enum xfs_defer_ops_type		dfp_type;
 };
 
-void xfs_defer_add(struct xfs_trans *tp, enum xfs_defer_ops_type type,
-		struct list_head *h);
+/*
+ * Create a log intent item for this deferred item, but don't actually finish
+ * the work.  Caller must clear this before the final transaction commit.
+ */
+#define XFS_DEFER_PAUSED	(1U << 0)
+
+#define XFS_DEFER_PENDING_STRINGS \
+	{ XFS_DEFER_PAUSED,	"paused" }
+
+void xfs_defer_item_pause(struct xfs_trans *tp, struct xfs_defer_pending *dfp);
+void xfs_defer_item_unpause(struct xfs_trans *tp, struct xfs_defer_pending *dfp);
+
+struct xfs_defer_pending *xfs_defer_add(struct xfs_trans *tp,
+		enum xfs_defer_ops_type type, struct list_head *h);
 int xfs_defer_finish_noroll(struct xfs_trans **tp);
 int xfs_defer_finish(struct xfs_trans **tp);
 int xfs_defer_finish_one(struct xfs_trans *tp, struct xfs_defer_pending *dfp);
-- 
2.44.0