xfs: update i_size after unwritten conversion in dio completion

Since commit d531d91d6990 ("xfs: always use unwritten extents for
direct I/O writes"), we start allocating unwritten extents for all
direct writes to allow appending aio in XFS.

But for dio writes that could extend file size we update the in-core
inode size first, then convert the unwritten extents to real
allocations at dio completion time in xfs_dio_write_end_io(). Thus a
racing direct read could see the new i_size and find the unwritten
extents first and read zeros instead of actual data, if the direct
writer also takes a shared iolock.

Fix it by updating the in-core inode size after the unwritten extent
conversion. To do this, introduce a new boolean argument to
xfs_iomap_write_unwritten() to tell if we want to update in-core
i_size or not.

Suggested-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

5 files changed, 28 insertions, 19 deletions

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 29172609f2a3..f18e5932aec4 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -343,7 +343,8 @@ xfs_end_io(
                 error = xfs_reflink_end_cow(ip, offset, size);
                 break;
         case XFS_IO_UNWRITTEN:
-                error = xfs_iomap_write_unwritten(ip, offset, size);
+                /* writeback should never update isize */
+                error = xfs_iomap_write_unwritten(ip, offset, size, false);
                 break;
         default:
                 ASSERT(!xfs_ioend_is_append(ioend) || ioend->io_append_trans);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 350b6d43ba23..309e26c9dddb 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -434,7 +434,6 @@ xfs_dio_write_end_io(
         struct inode            *inode = file_inode(iocb->ki_filp);
         struct xfs_inode        *ip = XFS_I(inode);
         loff_t                  offset = iocb->ki_pos;
-        bool                    update_size = false;
         int                     error = 0;
 
         trace_xfs_end_io_direct_write(ip, offset, size);
@@ -445,6 +444,21 @@ xfs_dio_write_end_io(
         if (size <= 0)
                 return size;
 
+        if (flags & IOMAP_DIO_COW) {
+                error = xfs_reflink_end_cow(ip, offset, size);
+                if (error)
+                        return error;
+        }
+
+        /*
+         * Unwritten conversion updates the in-core isize after extent
+         * conversion but before updating the on-disk size. Updating isize any
+         * earlier allows a racing dio read to find unwritten extents before
+         * they are converted.
+         */
+        if (flags & IOMAP_DIO_UNWRITTEN)
+                return xfs_iomap_write_unwritten(ip, offset, size, true);
+
         /*
          * We need to update the in-core inode size here so that we don't end up
          * with the on-disk inode size being outside the in-core inode size. We
@@ -459,20 +473,11 @@ xfs_dio_write_end_io(
         spin_lock(&ip->i_flags_lock);
         if (offset + size > i_size_read(inode)) {
                 i_size_write(inode, offset + size);
-                update_size = true;
-        }
-        spin_unlock(&ip->i_flags_lock);
-
-        if (flags & IOMAP_DIO_COW) {
-                error = xfs_reflink_end_cow(ip, offset, size);
-                if (error)
-                        return error;
-        }
-
-        if (flags & IOMAP_DIO_UNWRITTEN)
-                error = xfs_iomap_write_unwritten(ip, offset, size);
-        else if (update_size)
+                spin_unlock(&ip->i_flags_lock);
                 error = xfs_setfilesize(ip, offset, size);
+        } else {
+                spin_unlock(&ip->i_flags_lock);
+        }
 
         return error;
 }
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index a1909bc064e9..f179bdf1644d 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -829,7 +829,8 @@ int
 xfs_iomap_write_unwritten(
         xfs_inode_t     *ip,
         xfs_off_t       offset,
-        xfs_off_t       count)
+        xfs_off_t       count,
+        bool            update_isize)
 {
         xfs_mount_t     *mp = ip->i_mount;
         xfs_fileoff_t   offset_fsb;
@@ -840,6 +841,7 @@ xfs_iomap_write_unwritten(
         xfs_trans_t     *tp;
         xfs_bmbt_irec_t imap;
         struct xfs_defer_ops dfops;
+        struct inode    *inode = VFS_I(ip);
         xfs_fsize_t     i_size;
         uint            resblks;
         int             error;
@@ -899,7 +901,8 @@ xfs_iomap_write_unwritten(
                 i_size = XFS_FSB_TO_B(mp, offset_fsb + count_fsb);
                 if (i_size > offset + count)
                         i_size = offset + count;
-
+                if (update_isize && i_size > i_size_read(inode))
+                        i_size_write(inode, i_size);
                 i_size = xfs_new_eof(ip, i_size);
                 if (i_size) {
                         ip->i_d.di_size = i_size;
diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h
index 00db3ecea084..ee535065c5d0 100644
--- a/fs/xfs/xfs_iomap.h
+++ b/fs/xfs/xfs_iomap.h
@@ -27,7 +27,7 @@ int xfs_iomap_write_direct(struct xfs_inode *, xfs_off_t, size_t,
                         struct xfs_bmbt_irec *, int);
 int xfs_iomap_write_allocate(struct xfs_inode *, int, xfs_off_t,
                         struct xfs_bmbt_irec *);
-int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, xfs_off_t);
+int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, xfs_off_t, bool);
 
 void xfs_bmbt_to_iomap(struct xfs_inode *, struct iomap *,
                 struct xfs_bmbt_irec *);
diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
index 2f2dc3c09ad0..4246876df7b7 100644
--- a/fs/xfs/xfs_pnfs.c
+++ b/fs/xfs/xfs_pnfs.c
@@ -274,7 +274,7 @@ xfs_fs_commit_blocks(
                                         (end - 1) >> PAGE_SHIFT);
                 WARN_ON_ONCE(error);
 
-                error = xfs_iomap_write_unwritten(ip, start, length);
+                error = xfs_iomap_write_unwritten(ip, start, length, false);
                 if (error)
                         goto out_drop_iolock;
         }