On Fri, 22 Mar 2024, Ming Lei wrote:
> On Thu, Mar 21, 2024 at 05:48:45PM +0100, Mikulas Patocka wrote:
> > It may be possible to set up dm-integrity with smaller sector size than
> > the logical sector size of the underlying device. In this situation,
> > dm-integrity guarantees that the outgoing bios have the same alignment as
> > incoming bios (so, if you create a filesystem with 4k block size,
> > dm-integrity would send 4k-aligned bios to the underlying device).
> >
> > This guarantee was broken when integrity_recheck was implemented.
> > integrity_recheck sends bio that is aligned to ic->sectors_per_block. So
> > if we set up integrity with 512-byte sector size on a device with logical
> > block size 4k, we would be sending unaligned bio. This triggered a bug in
> > one of our internal tests.
> >
> > This commit fixes it - it determines what's the actual alignment of the
> > incoming bio and then makes sure that the outgoing bio in
> > integrity_recheck has the same alignment.
> >
> > Signed-off-by: Mikulas Patocka <[email protected]>
> > Fixes: c88f5e553fe3 ("dm-integrity: recheck the integrity tag after a
> > failure")
> > Cc: [email protected]
> >
> > ---
> > drivers/md/dm-integrity.c | 12 ++++++++++--
> > 1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > Index: linux-2.6/drivers/md/dm-integrity.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/md/dm-integrity.c 2024-03-21
> > 14:25:45.000000000 +0100
> > +++ linux-2.6/drivers/md/dm-integrity.c 2024-03-21 17:47:39.000000000
> > +0100
> > @@ -1699,7 +1699,6 @@ static noinline void integrity_recheck(s
> > struct bio_vec bv;
> > sector_t sector, logical_sector, area, offset;
> > struct page *page;
> > - void *buffer;
> >
> > get_area_and_offset(ic, dio->range.logical_sector, &area, &offset);
> > dio->metadata_block = get_metadata_sector_and_offset(ic, area, offset,
> > @@ -1708,13 +1707,14 @@ static noinline void integrity_recheck(s
> > logical_sector = dio->range.logical_sector;
> >
> > page = mempool_alloc(&ic->recheck_pool, GFP_NOIO);
> > - buffer = page_to_virt(page);
> >
> > __bio_for_each_segment(bv, bio, iter, dio->bio_details.bi_iter) {
> > unsigned pos = 0;
> >
> > do {
> > + sector_t alignment;
> > char *mem;
> > + char *buffer = page_to_virt(page);
> > int r;
> > struct dm_io_request io_req;
> > struct dm_io_region io_loc;
> > @@ -1727,6 +1727,14 @@ static noinline void integrity_recheck(s
> > io_loc.sector = sector;
> > io_loc.count = ic->sectors_per_block;
> >
> > + /* Align the bio to logical block size */
> > + alignment = dio->range.logical_sector |
> > bio_sectors(bio) | (PAGE_SIZE >> SECTOR_SHIFT);
> > + alignment &= -alignment;
>
> The above is less readable, :-(
It isolates the lowest bit from dio->range.logical_sector,
bio_sectors(bio) and (PAGE_SIZE >> SECTOR_SHIFT).
See for example this https://www.felixcloutier.com/x86/blsi
> > + io_loc.sector = round_down(io_loc.sector, alignment);
> > + io_loc.count += sector - io_loc.sector;
> > + buffer += (sector - io_loc.sector) << SECTOR_SHIFT;
> > + io_loc.count = round_up(io_loc.count, alignment);
>
> I feel the above code isn't very reliable, what we need actually is to
> make sure that io's sector & size is aligned with dm's
> bdev_logical_block_size(bdev).
I thought about using bdev_logical_block_size. But it may be wrong if the
device stack is reconfigured. So, I concluded that taking the alignment
from the bio would be better.
> Yeah, so far the max logical block size is 4k, but it may be increased
> in future and you can see the recent lsfmm proposal, so can we force it to be
> aligned with bdev_logical_block_size(bdev) here?
>
> Also can the above change work efficiently in case of 64K PAGE_SIZE?
It doesn't work efficiently at all - this piece of code is only run in a
pathological case where the user writes into a buffer while reading it (or
when he reads multiple blocks into the same buffer), so I optimized it for
size, not for performance.
But yes, it works with 64K PAGE_SIZE.
> Thanks,
> Ming
Mikulas
