On Sep 2, 2014, at 4:55 PM, NeilBrown <neilb@xxxxxxx> wrote: > On Tue, 2 Sep 2014 15:07:26 -0700 Eivind Sarto <eivindsarto@xxxxxxxxx> wrote: > >> >> On Sep 2, 2014, at 12:24 PM, Brassow Jonathan <jbrassow@xxxxxxxxxx> wrote: >> >>> >>> On Aug 29, 2014, at 2:29 PM, Eivind Sarto wrote: >>> >>>> I am seeing occasional data corruption during raid1 resync. >>>> Reviewing the raid1 code, I suspect that commit 79ef3a8aa1cb1523cc231c9a90a278333c21f761 introduced a bug. >>>> Prior to this commit raise_barrier() used to wait for conf->nr_pending to become zero. It no longer does this. >>>> It is not easy to reproduce the corruption, so I wanted to ask about the following potential fix while I am still testing it. >>>> Once I validate that the fix indeed works, I will post a proper patch. >>>> Do you have any feedback? >>>> >>>> — drivers/md/raid1.c 2014-08-22 15:19:15.000000000 -0700 >>>> +++ /tmp/raid1.c 2014-08-29 12:07:51.000000000 -0700 >>>> @@ -851,7 +851,7 @@ static void raise_barrier(struct r1conf >>>> * handling. >>>> */ >>>> wait_event_lock_irq(conf->wait_barrier, >>>> - !conf->array_frozen && >>>> + !conf->array_frozen && !conf->nr_pending && >>>> conf->barrier < RESYNC_DEPTH && >>>> (conf->start_next_window >= >>>> conf->next_resync + RESYNC_SECTORS), >>> >>> This patch does not work - at least, it doesn't fix the issues I'm seeing. My system hangs (in various places, like the resync thread) after commit 79ef3a8. When testing this patch, I also added some code to dm-raid.c to allow me to print-out some of the variables when I encounter a problem. After applying this patch and printing the variables, I see: >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: start_next_window = 12288 >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: current_window_requests = -46 >>> 5257 >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: next_window_requests = -11562 >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: nr_pending = 0 >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: nr_waiting = 0 >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: nr_queued = 0 >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: barrier = 1 >>> Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: array_frozen = 0 >>> >>> Some of those values look pretty bizarre to me and suggest the accounting is pretty messed up. >>> >>> brassow >>> >> >> After reviewing commit 79ef3a8aa1cb1523cc231c9a90a278333c21f761 I notice that wait_barrier() will now only exclude writes. User reads are not excluded even if the fall within the resync window. >> The old implementation used to exclude both reads and writes while resync-IO is active. >> Could this be a cause of data corruption? >> > > Could be. > From read_balance: > > if (conf->mddev->recovery_cp < MaxSector && > (this_sector + sectors >= conf->next_resync)) > choose_first = 1; > else > choose_first = 0; > > This used to be safe because a read immediately before next_resync would wait > until all resync requests completed. But now that read requests don't block > it isn't safe. > Probably best to make this: > > choose_first = (conf->mddev->recovery_cp < this_sector + sectors); > > Can you test that? > > Thanks, > NeilBrown I’ll give it a try. -eivind -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
