On Wed 19-12-12 02:27:10, Jan Kara wrote: > > With a u8 tid_t, the "else" clause from commit d9b0193 fires > > frequently; I really think the underlying problem is that tid_geq() > > etc does not properly handle wraparounds - if, say, target is 255 > > and j_commit_request is 0, we don't know if j_commit_request > > is 255 tids behind, or 1 tid ahead. I have to think about that > > some more, unless it's obvious to someone else. > Well, there's no way to handle wraps better AFAICT. Tids eventually wrap > and if someone has stored away tid of a transaction he wants committed and > keeps it for a long time before using it, it can end up being anywhere > before / after current j_commit_request. The hope was that it takes long > enough to wrap around 32-bit tids. If this happens often in practice we may > have to switch to 64-bit tids (in memory, on disk 32-bit tids are enough > because of limited journal size). > > > FWIW, some people have indeed seen that else clause fire upstream, > > both in the case where j_commit_request is > 2^31 and the > > target is 0. > > > > https://bugzilla.kernel.org/show_bug.cgi?id=46031 > > http://forums.debian.net/viewtopic.php?f=5&t=80741 > This is actually curious. The fact that i_datasync_tid was 0 means that > either journal was not initialized during ext3_iget() or j_commit_sequence > was 0 during ext3_iget() - note that j_commit_sequence is initialized to > j_transaction_sequence in journal_reset()... Hum, but in a case when > ext3_load_journal() calls journal_wipe() and that finds j_tail != 0, we > call journal_skip_recovery(). That ends up setting j_transaction_sequence > to the last transaction in the log but j_commit_sequence is left at 0. > I see that explains how we could hit the warning. I think we should > initialize j_commit_sequence properly also when skipping recovery and that > will solve the problem. Bah, I was wrong here. I misread ext3_journal_load(). We call journal_load() after journal_wipe() and so j_transaction_sequence and j_commit_sequence() are set properly... But then I don't see how i_datasync_tid was zero (modulo the very unlikely event we happened to load the inode just after wrapping tids). Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
