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List Info
Thread: Re: Re: device mapper not reporting no-barrier-support?
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| Re: Re: device mapper not reporting
no-barrier-support? |
 
Denmark |
2008-02-26 13:41:22 |
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 1und1.de> 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:
> > -309,7 +312,9 int blkdev_issue_flush(struct
block_device *bdev, sector_t *error_sector)
> > *error_sector = bio->bi_sector;
> >
> > ret = 0;
> > - if (!bio_flagged(bio, BIO_UPTODATE))
> > + if (bio_flagged(bio, BIO_EOPNOTSUPP))
> > + ret = -EOPNOTSUPP;
> > + else if (!bio_flagged(bio, BIO_UPTODATE))
> > ret = -EIO;
> >
> > bio_put(bio);
--
Jens Axboe
--
dm-devel mailing list
dm-develredhat.com
http
s://www.redhat.com/mailman/listinfo/dm-devel
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| Re: Re: device mapper not reporting
no-barrier-support? |
|
2008-02-26 14:20:30 |
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.henke1und1.de> 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).
Just for the records, the 2.6.24.2-ready version of your
patch:
---cut
--- linux-2.6.24.2/block/ll_rw_blk.c.prepatch 2008-02-11
06:51:11.000000000 +0
100
+++ linux-2.6.24.2/block/ll_rw_blk.c 2008-02-26
20:58:05.552467940 +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);
}
-2717,7
+2720,9
*error_sector = bio->bi_sector;
ret = 0;
- if (!bio_flagged(bio, BIO_UPTODATE))
+ if (bio_flagged(bio, BIO_EOPNOTSUPP))
+ ret = -EOPNOTSUPP;
+ else if (!bio_flagged(bio, BIO_UPTODATE))
ret = -EIO;
bio_put(bio);
---cut
Anders
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