[dm-devel] [PATCH] blk-settings: make sure that max_sectors is aligned on "logical_block_size" boundary.

[Mikulas Patocka]

On Thu, 19 Nov 2020, John Dorminy wrote:

> Greetings;
> 
> Might I suggest using SECTOR_SIZE instead of 512? Or, perhaps, >>
> SECTOR_SHIFT instead of / 512.

Yes, that's a good point.

> I don't understand the three conditionals. I believe max_sectors is
> supposed to be <= min(max_dev_sectors, max_hw_sectors), but I don't
> understand why max_sectors being small should adjust max_hw_sectors
> and max_dev_sectors. Are the conditions perhaps supposed to be
> different, adjusting each max_*sectors up to at least PAGE_SIZE /
> SECTOR_SIZE?

I copied this pattern from blk_queue_max_hw_sectors. Perhaps, we could 
use:
	t->max_sectors = round_down(t->max_sectors, t->logical_block_size / 512);
	if (!t->max_sectors)
		t->max_sectors = t->logical_block_size / 512;
instead.

Jens, what do you think is better?

Mikulas

> Perhaps, like e.g. blk_queue_max_hw_sectors(), the
> conditionals should log if they are adjusting max_*sectors up to the
> minimum.
> 
> Thanks!
> 
> John Dorminy
> 
> On Thu, Nov 19, 2020 at 3:37 PM Mikulas Patocka <mpatocka at redhat.com> wrote:
> >
> > We get these I/O errors when we run md-raid1 on the top of dm-integrity on
> > the top of ramdisk:
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0xff00, 0xff
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0xff00, 0xff
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0xffff, 0x1
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0xffff, 0x1
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0x8048, 0xff
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0x8147, 0xff
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0x8246, 0xff
> > device-mapper: integrity: Bio not aligned on 8 sectors: 0x8345, 0xbb
> >
> > The ramdisk device has logical_block_size 512 and max_sectors 255. The
> > dm-integrity device uses logical_block_size 4096 and it doesn't affect the
> > "max_sectors" value - thus, it inherits 255 from the ramdisk. So, we have
> > a device with max_sectors not aligned on logical_block_size.
> >
> > The md-raid device sees that the underlying leg has max_sectors 255 and it
> > will split the bios on 255-sector boundary, making the bios unaligned on
> > logical_block_size.
> >
> > In order to fix the bug, we round down max_sectors to logical_block_size.
> >
> > Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> > Cc: stable at vger.kernel.org
> >
> > ---
> >  block/blk-settings.c |   10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > Index: linux-2.6/block/blk-settings.c
> > ===================================================================
> > --- linux-2.6.orig/block/blk-settings.c 2020-10-29 12:20:46.000000000 +0100
> > +++ linux-2.6/block/blk-settings.c      2020-11-19 21:20:18.000000000 +0100
> > @@ -591,6 +591,16 @@ int blk_stack_limits(struct queue_limits
> >                 ret = -1;
> >         }
> >
> > +       t->max_sectors = round_down(t->max_sectors, t->logical_block_size / 512);
> > +       if (t->max_sectors < PAGE_SIZE / 512)
> > +               t->max_sectors = PAGE_SIZE / 512;
> > +       t->max_hw_sectors = round_down(t->max_hw_sectors, t->logical_block_size / 512);
> > +       if (t->max_sectors < PAGE_SIZE / 512)
> > +               t->max_hw_sectors = PAGE_SIZE / 512;
> > +       t->max_dev_sectors = round_down(t->max_dev_sectors, t->logical_block_size / 512);
> > +       if (t->max_sectors < PAGE_SIZE / 512)
> > +               t->max_dev_sectors = PAGE_SIZE / 512;
> > +
> >         /* Discard alignment and granularity */
> >         if (b->discard_granularity) {
> >                 alignment = queue_limit_discard_alignment(b, start);
> >
> > --
> > dm-devel mailing list
> > dm-devel at redhat.com
> > https://www.redhat.com/mailman/listinfo/dm-devel
> >
>