fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax…

… core While reviewing whether MAP_SYNC should strengthen its current guarantee of syncing writes from the initiating process to also include third-party readers observing dirty metadata, Dave pointed out that the check of IOMAP_WRITE is misplaced. The policy of what to with IOMAP_F_DIRTY should be separated from the generic filesystem mechanism of reporting dirty metadata. Move this policy to the fs-dax core to simplify the per-filesystem iomap handlers, and further centralize code that implements the MAP_SYNC policy. This otherwise should not change behavior, it just makes it easier to change behavior in the future. Reviewed-by: Jan Kara <[email protected]> Reviewed-by: Christoph Hellwig <[email protected]> Reviewed-by: Darrick J. Wong <[email protected]> Cc: Ross Zwisler <[email protected]> Reported-by: Dave Chinner <[email protected]> Signed-off-by: Dan Williams <[email protected]>
ambv · Nov 14, 2017 · aaa422c · aaa422c
1 parent a39e596
commit aaa422c
Show file tree

Hide file tree

Showing 3 changed files with 16 additions and 5 deletions.
diff --git a/fs/dax.c b/fs/dax.c
@@ -1079,6 +1079,17 @@ static int dax_fault_return(int error)
 	return VM_FAULT_SIGBUS;
 }
 
+/*
+ * MAP_SYNC on a dax mapping guarantees dirty metadata is
+ * flushed on write-faults (non-cow), but not read-faults.
+ */
+static bool dax_fault_is_synchronous(unsigned long flags,
+		struct vm_area_struct *vma, struct iomap *iomap)
+{
+	return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
+		&& (iomap->flags & IOMAP_F_DIRTY);
+}
+
 static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 			       const struct iomap_ops *ops)
 {
@@ -1170,7 +1181,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 		goto finish_iomap;
 	}
 
-	sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
+	sync = dax_fault_is_synchronous(flags, vma, &iomap);
 
 	switch (iomap.type) {
 	case IOMAP_MAPPED:
@@ -1390,7 +1401,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	if (iomap.offset + iomap.length < pos + PMD_SIZE)
 		goto finish_iomap;
 
-	sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
+	sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap);
 
 	switch (iomap.type) {
 	case IOMAP_MAPPED:

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
@@ -3479,7 +3479,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	}
 
 	iomap->flags = 0;
-	if ((flags & IOMAP_WRITE) && ext4_inode_datasync_dirty(inode))
+	if (ext4_inode_datasync_dirty(inode))
 		iomap->flags |= IOMAP_F_DIRTY;
 	iomap->bdev = inode->i_sb->s_bdev;
 	iomap->dax_dev = sbi->s_daxdev;

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
@@ -1087,8 +1087,8 @@ xfs_file_iomap_begin(
 		trace_xfs_iomap_found(ip, offset, length, 0, &imap);
 	}
 
-	if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
-	    (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
+	if (xfs_ipincount(ip) && (ip->i_itemp->ili_fsync_fields
+				& ~XFS_ILOG_TIMESTAMP))
 		iomap->flags |= IOMAP_F_DIRTY;
 
 	xfs_bmbt_to_iomap(ip, iomap, &imap);