diff options
authorJeff Mahoney <jeffm@suse.com>2013-09-23 16:50:42 -0400
committerJan Kara <jack@suse.cz>2013-09-24 11:24:21 +0200
commit721a769c034204e8e5f6ca4ecbff249e0225333b (patch)
parent7bc9cc07ee5bbac58bab88e8a5d6e32785f8fd32 (diff)
reiserfs: fix race with flush_used_journal_lists and flush_journal_list
There are two locks involved in managing the journal lists. The general reiserfs_write_lock and the journal->j_flush_mutex. While flush_journal_list is sleeping to acquire the j_flush_mutex or to submit a block for write, it will drop the write lock. This allows another thread to acquire the write lock and ultimately call flush_used_journal_lists to traverse the list of journal lists and select one for flushing. It can select the journal_list that has just had flush_journal_list called on it in the original thread and call it again with the same journal_list. The second thread then drops the write lock to acquire j_flush_mutex and the first thread reacquires it and continues execution and eventually clears and frees the journal list before dropping j_flush_mutex and returning. The second thread acquires j_flush_mutex and ends up operating on a journal_list that has already been released. If the memory hasn't been reused, we'll soon after hit a BUG_ON because the transaction id has already been cleared. If it's been reused, we'll crash in other fun ways. Since flush_journal_list will synchronize on j_flush_mutex, we can fix the race by taking a proper reference in flush_used_journal_lists and checking to see if it's still valid after the mutex is taken. It's safe to iterate the list of journal lists and pick a list with just the write lock as long as a reference is taken on the journal list before we drop the lock. We already have code to handle whether a transaction has been flushed already so we can use that to handle the race and get rid of the trans_id BUG_ON. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: Jan Kara <jack@suse.cz>
1 files changed, 4 insertions, 1 deletions
diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
index 7a37473b44dd..fd777032c2ba 100644
--- a/fs/reiserfs/journal.c
+++ b/fs/reiserfs/journal.c
@@ -1338,7 +1338,6 @@ static int flush_journal_list(struct super_block *s,
reiserfs_warning(s, "clm-2048", "called with wcount %d",
- BUG_ON(jl->j_trans_id == 0);
/* if flushall == 0, the lock is already held */
if (flushall) {
@@ -1765,6 +1764,8 @@ static int flush_used_journal_lists(struct super_block *s,
tjl = JOURNAL_LIST_ENTRY(tjl->j_list.next);
+ get_journal_list(jl);
+ get_journal_list(flush_jl);
/* try to find a group of blocks we can flush across all the
** transactions, but only bother if we've actually spanned
** across multiple lists
@@ -1773,6 +1774,8 @@ static int flush_used_journal_lists(struct super_block *s,
ret = kupdate_transactions(s, jl, &tjl, &trans_id, len, i);
flush_journal_list(s, flush_jl, 1);
+ put_journal_list(s, flush_jl);
+ put_journal_list(s, jl);
return 0;