On Tue 10-01-12 16:13:46, Surbhi Palande wrote: > >> If all the write operations were journaled, then this patch would not allow > >> ext4 filesystem to have any dirty data after its frozen. > >> (as journal_start() would block). > >> > >> I think the only one candidate that creates dirty data without calling > >> ext4_journal_start() is mmapped? > > No, the problem is in any write path. The problem is with operations > > that happen during the phase when s_frozen == SB_FREEZE_WRITE. These > > operations dirty the filesystem but running sync may easily miss them. > > During this phase journal is not frozen so that does not help you in any > > way. > > > > Honza > > Ok! No new transaction can really start after the journal is frozen. > But we can have dirty data after SB_FREEZE_WRITE and before > SB_FREEZE_TRANS. > I agree with you. However, can this be fixed by adding a > sync_filesystem() in freeze_super() after the sb->s_op->freeze_fs() is > over? The problem with this is that to do writeback you need to start a transaction. So you would deadlock. > So then essentially, when freeze_super() returns, the page cache is clean? > > I do definitely agree that the fix is to add a lock for mutual > exclusion between freeze filesystem and writes to a frozen filesystem. Yes, that would be the cleanest solution but it's quite some work. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
