On Mon, 1 Feb 2010, Takahiro Yasui wrote: > > This fixes bug https://bugzilla.redhat.com/show_bug.cgi?id=555197 > > > > Please submit this patch before 2.6.33 goes out. It fixes a bug when old > > LVM (<= 2.02.51) is used, that doesn't pass errors_handled flag to > > dm-raid1. > > > > It doesn't need to be backported to RHEL 5.5, because lvm always passes a > > flag to handle errors there. > > Don't we need to backport it to RHEL 5.5? If lvm is the only user of dm-raid1, > we don't need to backport it to RHEL 5.5. But if not, we need to. > > > Don't lose writes if errors are not handled and log fails > > > > If the log fails and errors are not handled by dmeventd, the writes > > are successfully finished without being actually written to the device. > > > > This code path is taken: > > do_writes: > > bio_list_merge(&ms->failures, &sync); > > do_failures: > > if (!get_valid_mirror(ms)) (false) > > else if (errors_handled(ms)) (false) > > else bio_endio(bio, 0); > > > > The logic in do_failures is based on presuming that the write was already > > tried --- if it succeeded at least on one leg and errors are not handled, > > it is reported as success. > > > > However, bio can be added to the failures queue without being submitted, in > > do_writes. > > > > This patch changes it so that bios are added to the failures list only if > > errors are handled --- then, they will be held with hold_bio() called from > > do_failures. > > I agree that bios should be issued by do_write() when ms->log_failures is set, > but do we need to add bios to the failures queue? As you mentioned, the failures > queue should be used to bios which are already handled. Therefore, I think > bios are better to handled directly by hold_bio() instead of adding them to > the failures queue as bios for nosync regions are done. > > - if (unlikely(ms->log_failure)) { > - spin_lock_irq(&ms->lock); > - bio_list_merge(&ms->failures, &sync); > - spin_unlock_irq(&ms->lock); > - wakeup_mirrord(ms); > - } else > - while ((bio = bio_list_pop(&sync))) > + while ((bio = bio_list_pop(&sync))) > + if (unlikely(ms->log_failure) && errors_handled(ms)) > + hold_bio(ms, bio); > + else > do_write(ms, bio); I thought about this too, but I'd decided to put the bios on the failures queue rather than holding them for this reason: if all the legs fail, it is better to terminate the bio with -EIO than to hold it. If all the legs fail, you can't save anything anyway and the less things you are holding, the less possibility for deadlocks exists. So I put the bios to the failure queue and do_failures will terminate them with -EIO if all the legs failred and hold them if we use dmeventd and there is at least one live leg. Mikulas > The policy to treat bios when ms->log_failures == 1 is different, but > the above code is based on the following patch. > > https://www.redhat.com/archives/dm-devel/2009-December/msg00211.html > > Thanks, > Taka > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
