[XFS] Fix to prevent the notorious 'NULL files' problem after a crash.

The problem that has been addressed is that of synchronising updates of
the file size with writes that extend a file. Without the fix the update
of a file's size, as a result of a write beyond eof, is independent of
when the cached data is flushed to disk. Often the file size update would
be written to the filesystem log before the data is flushed to disk. When
a system crashes between these two events and the filesystem log is
replayed on mount the file's size will be set but since the contents never
made it to disk the file is full of holes. If some of the cached data was
flushed to disk then it may just be a section of the file at the end that
has holes.

There are existing fixes to help alleviate this problem, particularly in
the case where a file has been truncated, that force cached data to be
flushed to disk when the file is closed. If the system crashes while the
file(s) are still open then this flushing will never occur.

The fix that we have implemented is to introduce a second file size,
called the in-memory file size, that represents the current file size as
viewed by the user. The existing file size, called the on-disk file size,
is the one that get's written to the filesystem log and we only update it
when it is safe to do so. When we write to a file beyond eof we only
update the in- memory file size in the write operation. Later when the I/O
operation, that flushes the cached data to disk completes, an I/O
completion routine will update the on-disk file size. The on-disk file
size will be updated to the maximum offset of the I/O or to the value of
the in-memory file size if the I/O includes eof.

SGI-PV: 958522
SGI-Modid: xfs-linux-melb:xfs-kern:28322a

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

1 files changed, 77 insertions, 12 deletions

diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index 143ffc851c9d..4475588e973a 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -141,9 +141,46 @@ xfs_destroy_ioend(
 }
 
 /*
+ * Update on-disk file size now that data has been written to disk.
+ * The current in-memory file size is i_size.  If a write is beyond
+ * eof io_new_size will be the intended file size until i_size is
+ * updated.  If this write does not extend all the way to the valid
+ * file size then restrict this update to the end of the write.
+ */
+STATIC void
+xfs_setfilesize(
+        xfs_ioend_t             *ioend)
+{
+        xfs_inode_t             *ip;
+        xfs_fsize_t             isize;
+        xfs_fsize_t             bsize;
+
+        ip = xfs_vtoi(ioend->io_vnode);
+
+        ASSERT((ip->i_d.di_mode & S_IFMT) == S_IFREG);
+        ASSERT(ioend->io_type != IOMAP_READ);
+
+        if (unlikely(ioend->io_error))
+                return;
+
+        bsize = ioend->io_offset + ioend->io_size;
+
+        xfs_ilock(ip, XFS_ILOCK_EXCL);
+
+        isize = MAX(ip->i_size, ip->i_iocore.io_new_size);
+        isize = MIN(isize, bsize);
+
+        if (ip->i_d.di_size < isize) {
+                ip->i_d.di_size = isize;
+                ip->i_update_core = 1;
+                ip->i_update_size = 1;
+        }
+
+        xfs_iunlock(ip, XFS_ILOCK_EXCL);
+}
+
+/*
  * Buffered IO write completion for delayed allocate extents.
- * TODO: Update ondisk isize now that we know the file data
- * has been flushed (i.e. the notorious "NULL file" problem).
  */
 STATIC void
 xfs_end_bio_delalloc(
@@ -152,6 +189,7 @@ xfs_end_bio_delalloc(
         xfs_ioend_t             *ioend =
                 container_of(work, xfs_ioend_t, io_work);
 
+        xfs_setfilesize(ioend);
         xfs_destroy_ioend(ioend);
 }
 
@@ -165,6 +203,7 @@ xfs_end_bio_written(
         xfs_ioend_t             *ioend =
                 container_of(work, xfs_ioend_t, io_work);
 
+        xfs_setfilesize(ioend);
         xfs_destroy_ioend(ioend);
 }
 
@@ -184,8 +223,23 @@ xfs_end_bio_unwritten(
         xfs_off_t               offset = ioend->io_offset;
         size_t                  size = ioend->io_size;
 
-        if (likely(!ioend->io_error))
+        if (likely(!ioend->io_error)) {
                 bhv_vop_bmap(vp, offset, size, BMAPI_UNWRITTEN, NULL, NULL);
+                xfs_setfilesize(ioend);
+        }
+        xfs_destroy_ioend(ioend);
+}
+
+/*
+ * IO read completion for regular, written extents.
+ */
+STATIC void
+xfs_end_bio_read(
+        struct work_struct      *work)
+{
+        xfs_ioend_t             *ioend =
+                container_of(work, xfs_ioend_t, io_work);
+
         xfs_destroy_ioend(ioend);
 }
 
@@ -224,6 +278,8 @@ xfs_alloc_ioend(
                 INIT_WORK(&ioend->io_work, xfs_end_bio_unwritten);
         else if (type == IOMAP_DELAY)
                 INIT_WORK(&ioend->io_work, xfs_end_bio_delalloc);
+        else if (type == IOMAP_READ)
+                INIT_WORK(&ioend->io_work, xfs_end_bio_read);
         else
                 INIT_WORK(&ioend->io_work, xfs_end_bio_written);
 
@@ -913,7 +969,7 @@ xfs_page_state_convert(
         bh = head = page_buffers(page);
         offset = page_offset(page);
         flags = -1;
-        type = 0;
+        type = IOMAP_READ;
 
         /* TODO: cleanup count and page_dirty */
 
@@ -999,7 +1055,7 @@ xfs_page_state_convert(
                          * That means it must already have extents allocated
                          * underneath it. Map the extent by reading it.
                          */
-                        if (!iomap_valid || type != 0) {
+                        if (!iomap_valid || type != IOMAP_READ) {
                                 flags = BMAPI_READ;
                                 size = xfs_probe_cluster(inode, page, bh,
                                                                 head, 1);
@@ -1010,7 +1066,7 @@ xfs_page_state_convert(
                                 iomap_valid = xfs_iomap_valid(&iomap, offset);
                         }
 
-                        type = 0;
+                        type = IOMAP_READ;
                         if (!test_and_set_bit(BH_Lock, &bh->b_state)) {
                                 ASSERT(buffer_mapped(bh));
                                 if (iomap_valid)
@@ -1356,12 +1412,21 @@ xfs_end_io_direct(
          * completion handler in the future, in which case all this can
          * go away.
          */
-        if (private && size > 0) {
-                ioend->io_offset = offset;
-                ioend->io_size = size;
+        ioend->io_offset = offset;
+        ioend->io_size = size;
+        if (ioend->io_type == IOMAP_READ) {
+                xfs_finish_ioend(ioend);
+        } else if (private && size > 0) {
                 xfs_finish_ioend(ioend);
         } else {
-                xfs_destroy_ioend(ioend);
+                /*
+                 * A direct I/O write ioend starts it's life in unwritten
+                 * state in case they map an unwritten extent.  This write
+                 * didn't map an unwritten extent so switch it's completion
+                 * handler.
+                 */
+                INIT_WORK(&ioend->io_work, xfs_end_bio_written);
+                xfs_finish_ioend(ioend);
         }
 
         /*
@@ -1392,15 +1457,15 @@ xfs_vm_direct_IO(
         if (error)
                 return -error;
 
-        iocb->private = xfs_alloc_ioend(inode, IOMAP_UNWRITTEN);
-
         if (rw == WRITE) {
+                iocb->private = xfs_alloc_ioend(inode, IOMAP_UNWRITTEN);
                 ret = blockdev_direct_IO_own_locking(rw, iocb, inode,
                         iomap.iomap_target->bt_bdev,
                         iov, offset, nr_segs,
                         xfs_get_blocks_direct,
                         xfs_end_io_direct);
         } else {
+                iocb->private = xfs_alloc_ioend(inode, IOMAP_READ);
                 ret = blockdev_direct_IO_no_locking(rw, iocb, inode,
                         iomap.iomap_target->bt_bdev,
                         iov, offset, nr_segs,