3 files changed, 25 insertions, 3 deletions
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 34de6e6898c4..f11ef331e5a4 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -1171,6 +1171,12 @@ xfs_iread_extents(
 		goto out;
 	}
 	ASSERT(ir.loaded == xfs_iext_count(ifp));
+	/*
+	 * Use release semantics so that we can use acquire semantics in
+	 * xfs_need_iread_extents and be guaranteed to see a valid mapping tree
+	 * after that load.
+	 */
+	smp_store_release(&ifp->if_needextents, 0);
 	return 0;
 out:
 	xfs_iext_destroy(ifp);
diff --git a/fs/xfs/libxfs/xfs_inode_fork.c b/fs/xfs/libxfs/xfs_inode_fork.c
index 6b21760184d9..1bbe5ea3f00b 100644
--- a/fs/xfs/libxfs/xfs_inode_fork.c
+++ b/fs/xfs/libxfs/xfs_inode_fork.c
@@ -226,10 +226,15 @@ xfs_iformat_data_fork(
 
 	/*
 	 * Initialize the extent count early, as the per-format routines may
-	 * depend on it.
+	 * depend on it.  Use release semantics to set needextents /after/ we
+	 * set the format. This ensures that we can use acquire semantics on
+	 * needextents in xfs_need_iread_extents() and be guaranteed to see a
+	 * valid format value after that load.
 	 */
 	ip->i_df.if_format = dip->di_format;
 	ip->i_df.if_nextents = xfs_dfork_data_extents(dip);
+	smp_store_release(&ip->i_df.if_needextents,
+			   ip->i_df.if_format == XFS_DINODE_FMT_BTREE ? 1 : 0);
 
 	switch (inode->i_mode & S_IFMT) {
 	case S_IFIFO:
@@ -282,8 +287,17 @@ xfs_ifork_init_attr(
 	enum xfs_dinode_fmt	format,
 	xfs_extnum_t		nextents)
 {
+	/*
+	 * Initialize the extent count early, as the per-format routines may
+	 * depend on it.  Use release semantics to set needextents /after/ we
+	 * set the format. This ensures that we can use acquire semantics on
+	 * needextents in xfs_need_iread_extents() and be guaranteed to see a
+	 * valid format value after that load.
+	 */
 	ip->i_af.if_format = format;
 	ip->i_af.if_nextents = nextents;
+	smp_store_release(&ip->i_af.if_needextents,
+			   ip->i_af.if_format == XFS_DINODE_FMT_BTREE ? 1 : 0);
 }
 
 void
diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
index d3943d6ad0b9..96d307784c85 100644
--- a/fs/xfs/libxfs/xfs_inode_fork.h
+++ b/fs/xfs/libxfs/xfs_inode_fork.h
@@ -24,6 +24,7 @@ struct xfs_ifork {
 	xfs_extnum_t		if_nextents;	/* # of extents in this fork */
 	short			if_broot_bytes;	/* bytes allocated for root */
 	int8_t			if_format;	/* format of this fork */
+	uint8_t			if_needextents;	/* extents have not been read */
 };
 
 /*
@@ -260,9 +261,10 @@ int xfs_iext_count_upgrade(struct xfs_trans *tp, struct xfs_inode *ip,
 		uint nr_to_add);
 
 /* returns true if the fork has extents but they are not read in yet. */
-static inline bool xfs_need_iread_extents(struct xfs_ifork *ifp)
+static inline bool xfs_need_iread_extents(const struct xfs_ifork *ifp)
 {
-	return ifp->if_format == XFS_DINODE_FMT_BTREE && ifp->if_height == 0;
+	/* see xfs_iformat_{data,attr}_fork() for needextents semantics */
+	return smp_load_acquire(&ifp->if_needextents) != 0;
 }
 
 #endif	/* __XFS_INODE_FORK_H__ */