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SubjectRe: Bug in ext3
Hi,

On Thu, Nov 15, 2001 at 04:21:49PM -0700, Andreas Dilger wrote:

> I don't disagree that something corrupted it, but it is hard to tell from
> here what it could be. Looking at ext3_read_super(), it is pretty much
> a read-only path, except journal recovery. If, for some reason, you had
> an old, unrecovered ext3 journal in the fs, it is possible that recovering
> from it would corrupt your fs by writing old data into the fs.

Except that can only happen once we have found a journal to recover,
and the error that ext3 spat out indicated that it couldn't find a
journal at all and was giving up.

> Looking at the ext3_read_super() path, we call ext3_load_journal(),
> which calls journal_wipe() and journal_load(), which both call
> journal_load()->load_superblock()->journal_get_superblock(), which
> gives us the two "JBD: no valid journal superblock found" messages,
> and return errors before doing anything else. Then we get the message
> "EXT3-fs: error loading journal." and return without mounting the fs.

Indeed.

> Hmm, there is a possibility that journal_destroy() calling
> journal_update_superblock() scribbling data into the first block of
> the old "journal". Stephen, Andrew, we need to exit from the
> journal_get_superblock() with j_sb_buffer = NULL, and then check for
> this in journal_destroy() so we don't call journal_update_superblock().
> How does the below patch look?

Looks OK. I've done a slightly better version which catches a couple
of extra cases but it's basically the same solution. I've also added
a tiny patch to prevent a failed journal_wipe() from being followed by
a journal_load() attempt, so we don't get the same error twice.

Patch below.

Cheers,
Stephen
Index: fs/ext3/super.c
===================================================================
RCS file: /cvsroot/gkernel/ext3/fs/ext3/super.c,v
retrieving revision 1.34.2.11
diff -u -r1.34.2.11 super.c
--- fs/ext3/super.c 2001/10/27 03:34:03 1.34.2.11
+++ fs/ext3/super.c 2001/11/16 18:30:39
@@ -1350,7 +1350,7 @@
journal_t *journal;
int journal_inum = le32_to_cpu(es->s_journal_inum);
int journal_dev = le32_to_cpu(es->s_journal_dev);
- int err;
+ int err = 0;
int really_read_only;

really_read_only = is_read_only(sb->s_dev);
@@ -1400,9 +1400,10 @@
}

if (!EXT3_HAS_INCOMPAT_FEATURE(sb, EXT3_FEATURE_INCOMPAT_RECOVER))
- journal_wipe(journal, !really_read_only);
+ err = journal_wipe(journal, !really_read_only);
+ if (!err)
+ err = journal_load(journal);

- err = journal_load(journal);
if (err) {
printk(KERN_ERR "EXT3-fs: error loading journal.\n");
journal_destroy(journal);
Index: fs/jbd/journal.c
===================================================================
RCS file: /cvsroot/gkernel/ext3/fs/jbd/journal.c,v
retrieving revision 1.49.2.6
diff -u -r1.49.2.6 journal.c
--- fs/jbd/journal.c 2001/11/16 14:45:21 1.49.2.6
+++ fs/jbd/journal.c 2001/11/16 18:30:42
@@ -773,6 +773,18 @@
return journal;
}

+/*
+ * If the journal init or create aborts, we need to mark the journal
+ * superblock as being NULL to prevent the journal destroy from writing
+ * back a bogus superblock.
+ */
+static void journal_fail_superblock (journal_t *journal)
+{
+ struct buffer_head *bh = journal->j_sb_buffer;
+ brelse(bh);
+ journal->j_sb_buffer = NULL;
+}
+
/*
* Given a journal_t structure, initialise the various fields for
* startup of a new journaling session. We use this both when creating
@@ -826,6 +838,7 @@
if (journal->j_maxlen < JFS_MIN_JOURNAL_BLOCKS) {
printk (KERN_ERR "Journal length (%d blocks) too short.\n",
journal->j_maxlen);
+ journal_fail_superblock(journal);
return -EINVAL;
}

@@ -916,7 +929,8 @@
{
struct buffer_head *bh;
journal_superblock_t *sb;
-
+ int err = -EIO;
+
bh = journal->j_sb_buffer;

J_ASSERT(bh != NULL);
@@ -926,16 +940,18 @@
if (!buffer_uptodate(bh)) {
printk (KERN_ERR
"JBD: IO error reading journal superblock\n");
- return -EIO;
+ goto out;
}
}

sb = journal->j_superblock;

+ err = -EINVAL;
+
if (sb->s_header.h_magic != htonl(JFS_MAGIC_NUMBER) ||
sb->s_blocksize != htonl(journal->j_blocksize)) {
printk(KERN_WARNING "JBD: no valid journal superblock found\n");
- return -EINVAL;
+ goto out;
}

switch(ntohl(sb->s_header.h_blocktype)) {
@@ -947,17 +963,21 @@
break;
default:
printk(KERN_WARNING "JBD: unrecognised superblock format ID\n");
- return -EINVAL;
+ goto out;
}

if (ntohl(sb->s_maxlen) < journal->j_maxlen)
journal->j_maxlen = ntohl(sb->s_maxlen);
else if (ntohl(sb->s_maxlen) > journal->j_maxlen) {
printk (KERN_WARNING "JBD: journal file too short\n");
- return -EINVAL;
+ goto out;
}

return 0;
+
+out:
+ journal_fail_superblock(journal);
+ return err;
}

/*
@@ -1062,7 +1082,10 @@
/* We can now mark the journal as empty. */
journal->j_tail = 0;
journal->j_tail_sequence = ++journal->j_transaction_sequence;
- journal_update_superblock(journal, 1);
+ if (journal->j_sb_buffer) {
+ journal_update_superblock(journal, 1);
+ brelse(journal->j_sb_buffer);
+ }

if (journal->j_inode)
iput(journal->j_inode);
@@ -1070,7 +1093,6 @@
journal_destroy_revoke(journal);

unlock_journal(journal);
- brelse(journal->j_sb_buffer);
kfree(journal);
MOD_DEC_USE_COUNT;
}
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