path: root/fs/udf/super.c
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)
treef73faca4b745d8250d09708781455d59bf65168d /fs/udf/super.c
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>
Diffstat (limited to 'fs/udf/super.c')
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