On Tue, Feb 26 2008, Anders Henke wrote: > On Tue, Feb 26 2008 schrieb Jens Axboe: > > On Tue, Feb 26 2008, Anders Henke wrote: > > > On Tue, Feb 26 2008 Jens Axboe wrote: > > > > On Tue, Feb 26 2008, Alasdair G Kergon wrote: > > > > > On Mon, Feb 25, 2008 at 03:20:50PM -0800, Andrew Morton wrote: > > > > > > On Mon, 25 Feb 2008 14:26:15 +0100 Anders Henke <anders.henke@xxxxxxxx> wrote: > > > > > > > I'm currently stuck between Kernel LVM and DRBD, as I'm using Kernel > > > > > > > 2.6.24.2 with DRBD 8.2.5 on top of an LVM2 device (LV). > > > > > > > -LVM2/device mapper doesn't support write barriers > > > > > > > > > > That's right. > > > > > > > > > > > > -DRBD uses blkdev_issue_flush() to flush its metadata to disk. > > > > > > > > > > Which won't work if device-mapper is underneath. > > > > > > > > > > > > On a no-barrier-device, DRBD should receive EOPNOTSUPP, but > > > > > > > it really does receive an EIO. Promptly, DRBD gives the > > > > > > > error message "drbd0: local disk flush failed with status -5". > > > > > > > I've posted a lengty summary of my findings to > > > > > > > http://lists.linbit.com/pipermail/drbd-user/2008-February/008665.html > > > > > > > ... that DRBD does catch the EOPNOTSUPP for blkdev_issue_flush and > > > > > > > BIO_RW_BARRIER, but the lvm implementation of blkdev_issue_flush in > > > > > > > 2.6.24.2 aparently does return EIO for blkdev_issue_flush. > > > > > > I'd say it's a DM bug. > > > > > > > > > > The dm code is unchanged, but look at the limited endio handling in > > > > > ll_rw_blk.c: > > > > > > > > > > static void bio_end_empty_barrier(struct bio *bio, int err) > > > > > { > > > > > if (err) > > > > > clear_bit(BIO_UPTODATE, &bio->bi_flags); > > > > > > > > > > complete(bio->bi_private); > > > > > } > > > > > > > > > > int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector) > > > > > { > > > > > ... > > > > > wait_for_completion(&wait); > > > > > if (error_sector) > > > > > *error_sector = bio->bi_sector; > > > > > ret = 0; > > > > > if (!bio_flagged(bio, BIO_UPTODATE)) > > > > > ret = -EIO; > > > > > > > > You are right, the return value got broken there. Does this make it > > > > return -EOPNOTSUPP properly for you? > > > > > > > > > No, it doesn't. > > > > > > > > > > > > I've applied your patch manually, as 2.6.24.2. doesn't have a "blk-barrier.c": > > > > > > ---cut > > > --- linux-2.6.24.2/block/ll_rw_blk.c.prepatch 2008-02-11 > > > 06:51:11.000000000 +0100 > > > +++ linux-2.6.24.2/block/ll_rw_blk.c 2008-02-26 20:02:28.514641620 > > > +0100 > > > @@ -2667,8 +2667,11 @@ > > > > > > static void bio_end_empty_barrier(struct bio *bio, int err) > > > { > > > - if (err) > > > + if (err) { > > > + if (err == -EOPNOTSUPP) > > > + set_bit(BIO_EOPNOTSUPP, &bio->bi_flags); > > > clear_bit(BIO_UPTODATE, &bio->bi_flags); > > > + } > > > > > > complete(bio->bi_private); > > > } > > > ---cut > > > > > > ... and the resulting kernel shows exactly the same behaviour than before: > > > > Not surprising, as you missed half of the patch: > > Ouch. Thank you for pointing this out. > > I've been spending too much time of the day with things who have a negative > impact on my concentration and I shouldn't manually patch kernels at > this time of the day. > > Yes, it's useless to set a bit, but never check it (like in my version of > your patch). > > After adding the second part of your patch, the resulting kernel works as > intended: > > [ 234.946192] drbd0: conn( WFSyncUUID -> SyncTarget ) > [ 234.956176] drbd0: Began resync as SyncTarget (will sync 19542404 KB > [4885601 > bits set]). > [ 234.972567] drbd0: Writing meta data super block now. > [ 235.018203] drbd0: local disk flush failed with status -95 > > DRBD sees the EOPNOTSUPP, logs this message only once and doesn't try > any further barrier requests (as intended). OK good, that's what I expected :-) I'll queue the patch for 2.6.25, the 2.6.24 should go to stable. Send me a properly formatted patch and I'll make sure it goes that way. Thanks for testing! -- Jens Axboe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
