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authorJan Kara <jack@suse.cz>2009-02-10 11:15:34 -0500
committerTheodore Tso <tytso@mit.edu>2009-02-10 11:15:34 -0500
commit7f5aa215088b817add9c71914b83650bdd49f8a9 (patch)
tree9b811d1f0b41a2738fc68654ae605bf5d8cf2a72 /fs/jbd2
parent9eddacf9e9c03578ef2c07c9534423e823d677f8 (diff)
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jbd2: Avoid possible NULL dereference in jbd2_journal_begin_ordered_truncate()
If we race with commit code setting i_transaction to NULL, we could possibly dereference it. Proper locking requires the journal pointer (to access journal->j_list_lock), which we don't have. So we have to change the prototype of the function so that filesystem passes us the journal pointer. Also add a more detailed comment about why the function jbd2_journal_begin_ordered_truncate() does what it does and how it should be used. Thanks to Dan Carpenter <error27@gmail.com> for pointing to the suspitious code. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Acked-by: Joel Becker <joel.becker@oracle.com> CC: linux-ext4@vger.kernel.org CC: ocfs2-devel@oss.oracle.com CC: mfasheh@suse.de CC: Dan Carpenter <error27@gmail.com>
Diffstat (limited to 'fs/jbd2')
-rw-r--r--fs/jbd2/transaction.c42
1 files changed, 31 insertions, 11 deletions
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 46b4e34..28ce21d 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -2129,26 +2129,46 @@ done:
}
/*
- * This function must be called when inode is journaled in ordered mode
- * before truncation happens. It starts writeout of truncated part in
- * case it is in the committing transaction so that we stand to ordered
- * mode consistency guarantees.
+ * File truncate and transaction commit interact with each other in a
+ * non-trivial way. If a transaction writing data block A is
+ * committing, we cannot discard the data by truncate until we have
+ * written them. Otherwise if we crashed after the transaction with
+ * write has committed but before the transaction with truncate has
+ * committed, we could see stale data in block A. This function is a
+ * helper to solve this problem. It starts writeout of the truncated
+ * part in case it is in the committing transaction.
+ *
+ * Filesystem code must call this function when inode is journaled in
+ * ordered mode before truncation happens and after the inode has been
+ * placed on orphan list with the new inode size. The second condition
+ * avoids the race that someone writes new data and we start
+ * committing the transaction after this function has been called but
+ * before a transaction for truncate is started (and furthermore it
+ * allows us to optimize the case where the addition to orphan list
+ * happens in the same transaction as write --- we don't have to write
+ * any data in such case).
*/
-int jbd2_journal_begin_ordered_truncate(struct jbd2_inode *inode,
+int jbd2_journal_begin_ordered_truncate(journal_t *journal,
+ struct jbd2_inode *jinode,
loff_t new_size)
{
- journal_t *journal;
- transaction_t *commit_trans;
+ transaction_t *inode_trans, *commit_trans;
int ret = 0;
- if (!inode->i_transaction && !inode->i_next_transaction)
+ /* This is a quick check to avoid locking if not necessary */
+ if (!jinode->i_transaction)
goto out;
- journal = inode->i_transaction->t_journal;
+ /* Locks are here just to force reading of recent values, it is
+ * enough that the transaction was not committing before we started
+ * a transaction adding the inode to orphan list */
spin_lock(&journal->j_state_lock);
commit_trans = journal->j_committing_transaction;
spin_unlock(&journal->j_state_lock);
- if (inode->i_transaction == commit_trans) {
- ret = filemap_fdatawrite_range(inode->i_vfs_inode->i_mapping,
+ spin_lock(&journal->j_list_lock);
+ inode_trans = jinode->i_transaction;
+ spin_unlock(&journal->j_list_lock);
+ if (inode_trans == commit_trans) {
+ ret = filemap_fdatawrite_range(jinode->i_vfs_inode->i_mapping,
new_size, LLONG_MAX);
if (ret)
jbd2_journal_abort(journal, ret);