[062/105] UBIFS: fix debugging failure in dbg_check_space_info

Greg KH
2011-04-12T14:38:29Z

From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

commit 7da6443aca9be29c6948dcbd636ad50154d0bc0c upstream.

This patch fixes a debugging failure with which looks like this:
UBIFS error (pid 32313): dbg_check_space_info: free space changed from 6019344 to 6022654

The reason for this failure is described in the comment this patch adds
to the code. But in short - 'c->freeable_cnt' may be different before
and after re-mounting, and this is normal. So the debugging code should
make sure that free space calculations do not depend on 'c->freeable_cnt'.

A similar issue has been reported here:
http://lists.infradead.org/pipermail/linux-mtd/2011-April/034647.html

This patch should fix it.

For the -stable guys: this patch is only relevant for kernels 2.6.30
onwards.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/ubifs/debug.c | 41 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 36 insertions(+), 5 deletions(-)

--- a/fs/ubifs/debug.c
+++ b/fs/ubifs/debug.c
@@ -961,11 +961,39 @@ void dbg_dump_index(struct ubifs_info *c
void dbg_save_space_info(struct ubifs_info *c)
{
struct ubifs_debug_info *d = c->dbg;
-
- ubifs_get_lp_stats(c, &d->saved_lst);
+ int freeable_cnt;

spin_lock(&c->space_lock);
+ memcpy(&d->saved_lst, &c->lst, sizeof(struct ubifs_lp_stats));
+
+ /*
+ * We use a dirty hack here and zero out @c->freeable_cnt, because it
+ * affects the free space calculations, and UBIFS might not know about
+ * all freeable eraseblocks. Indeed, we know about freeable eraseblocks
+ * only when we read their lprops, and we do this only lazily, upon the
+ * need. So at any given point of time @c->freeable_cnt might be not
+ * exactly accurate.
+ *
+ * Just one example about the issue we hit when we did not zero
+ * @c->freeable_cnt.
+ * 1. The file-system is mounted R/O, c->freeable_cnt is %0. We save the
+ * amount of free space in @d->saved_free
+ * 2. We re-mount R/W, which makes UBIFS to read the "lsave"
+ * information from flash, where we cache LEBs from various
+ * categories ('ubifs_remount_fs()' -> 'ubifs_lpt_init()'
+ * -> 'lpt_init_wr()' -> 'read_lsave()' -> 'ubifs_lpt_lookup()'
+ * -> 'ubifs_get_pnode()' -> 'update_cats()'
+ * -> 'ubifs_add_to_cat()').
+ * 3. Lsave contains a freeable eraseblock, and @c->freeable_cnt
+ * becomes %1.
+ * 4. We calculate the amount of free space when the re-mount is
+ * finished in 'dbg_check_space_info()' and it does not match
+ * @d->saved_free.
+ */
+ freeable_cnt = c->freeable_cnt;
+ c->freeable_cnt = 0;
d->saved_free = ubifs_get_free_space_nolock(c);
+ c->freeable_cnt = freeable_cnt;
spin_unlock(&c->space_lock);
}

@@ -982,12 +1010,15 @@ int dbg_check_space_info(struct ubifs_in
{
struct ubifs_debug_info *d = c->dbg;
struct ubifs_lp_stats lst;
- long long avail, free;
+ long long free;
+ int freeable_cnt;

spin_lock(&c->space_lock);
- avail = ubifs_calc_available(c, c->min_idx_lebs);
+ freeable_cnt = c->freeable_cnt;
+ c->freeable_cnt = 0;
+ free = ubifs_get_free_space_nolock(c);
+ c->freeable_cnt = freeable_cnt;
spin_unlock(&c->space_lock);
- free = ubifs_get_free_space(c);

if (free != d->saved_free) {
ubifs_err("free space changed from %lld to %lld",