UBIFS: make space fixup work in the remount case

The UBIFS space fixup is a useful feature which allows to fixup the "broken"
flash space at the time of the first mount. The "broken" space is usually the
result of using a "dumb" industrial flasher which is not able to skip empty
NAND pages and just writes all 0xFFs to the empty space, which has grave
side-effects for UBIFS when UBIFS trise to write useful data to those empty
pages.

The fix-up feature works roughly like this:
1. mkfs.ubifs sets the fixup flag in UBIFS superblock when creating the image
   (see -F option)
2. when the file-system is mounted for the first time, UBIFS notices the fixup
   flag and re-writes the entire media atomically, which may take really a lot
   of time.
3. UBIFS clears the fixup flag in the superblock.

This works fine when the file system is mounted R/W for the very first time.
But it did not really work in the case when we first mount the file-system R/O,
and then re-mount R/W. The reason was that we started the fixup procedure too
late, which we cannot really do because we have to fixup the space before it
starts being used.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reported-by: Mark Jackson <mpfj-list@mimc.co.uk>
Cc: stable@vger.kernel.org # 3.0+

diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index ac838b8..f21acf0 100644 (file)
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1568,6 +1568,12 @@ static int ubifs_remount_rw(struct ubifs_info *c)
        c->remounting_rw = 1;
        c->ro_mount = 0;
 
+       if (c->space_fixup) {
+               err = ubifs_fixup_free_space(c);
+               if (err)
+                       return err;
+       }
+
        err = check_free_space(c);
        if (err)
                goto out;
@@ -1684,12 +1690,6 @@ static int ubifs_remount_rw(struct ubifs_info *c)
                err = dbg_check_space_info(c);
        }
 
-       if (c->space_fixup) {
-               err = ubifs_fixup_free_space(c);
-               if (err)
-                       goto out;
-       }
-
        mutex_unlock(&c->umount_mutex);
        return err;