On Tue, 14 Apr 2020, Mike Snitzer wrote:
> On Wed, Apr 08 2020 at 3:02pm -0400,
> Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
> > The dm-writecache reads metadata in the target constructor. However, when
> > we reload the target, there could be another active instance running on
> > the same device. This is the sequence of operations when doing a reload:
> >
> > 1. construct new target
> > 2. suspend old target
> > 3. resume new target
> > 4. destroy old target
> >
> > Metadata that were written by the old target between steps 1 and 2 would
> > not be visible by the new target.
> >
> > This patch fixes the data corruption by loading the metadata in the resume
> > handler.
> >
> > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx # v4.18+
> > Fixes: 48debafe4f2f ("dm: add writecache target")
> >
> > ---
> > drivers/md/dm-writecache.c | 44 ++++++++++++++++++++++++++++++--------------
> > 1 file changed, 30 insertions(+), 14 deletions(-)
> >
> > Index: linux-2.6/drivers/md/dm-writecache.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/md/dm-writecache.c 2020-04-08 14:47:17.000000000 +0200
> > +++ linux-2.6/drivers/md/dm-writecache.c 2020-04-08 20:59:15.000000000 +0200
> > @@ -931,6 +931,24 @@ static int writecache_alloc_entries(stru
> > return 0;
> > }
> >
> > +static int writecache_read_metadata(struct dm_writecache *wc, sector_t n_sectors)
> > +{
> > + struct dm_io_region region;
> > + struct dm_io_request req;
> > +
> > + region.bdev = wc->ssd_dev->bdev;
> > + region.sector = wc->start_sector;
> > + region.count = wc->metadata_sectors;
> > + req.bi_op = REQ_OP_READ;
> > + req.bi_op_flags = REQ_SYNC;
> > + req.mem.type = DM_IO_VMA;
> > + req.mem.ptr.vma = (char *)wc->memory_map;
> > + req.client = wc->dm_io;
> > + req.notify.fn = NULL;
> > +
> > + return dm_io(&req, 1, ®ion, NULL);
> > +}
> > +
>
> You aren't using the passed n_sectors (for region.count?)
>
>
> > static void writecache_resume(struct dm_target *ti)
> > {
> > struct dm_writecache *wc = ti->private;
> > @@ -941,8 +959,16 @@ static void writecache_resume(struct dm_
> >
> > wc_lock(wc);
> >
> > - if (WC_MODE_PMEM(wc))
> > + if (WC_MODE_PMEM(wc)) {
> > persistent_memory_invalidate_cache(wc->memory_map, wc->memory_map_size);
> > + } else {
> > + r = writecache_read_metadata(wc, wc->metadata_sectors);
> > + if (r) {
> > + writecache_error(wc, r, "unable to read metadata: %d", r);
> > + memset((char *)wc->memory_map + offsetof(struct wc_memory_superblock, entries), -1,
> > + (wc->metadata_sectors << SECTOR_SHIFT) - offsetof(struct wc_memory_superblock, entries));
> > + }
> > + }
> >
> > wc->tree = RB_ROOT;
> > INIT_LIST_HEAD(&wc->lru);
> > @@ -2200,8 +2226,6 @@ invalid_optional:
> > goto bad;
> > }
> > } else {
> > - struct dm_io_region region;
> > - struct dm_io_request req;
> > size_t n_blocks, n_metadata_blocks;
> > uint64_t n_bitmap_bits;
> >
> > @@ -2258,17 +2282,9 @@ invalid_optional:
> > goto bad;
> > }
> >
> > - region.bdev = wc->ssd_dev->bdev;
> > - region.sector = wc->start_sector;
> > - region.count = wc->metadata_sectors;
> > - req.bi_op = REQ_OP_READ;
> > - req.bi_op_flags = REQ_SYNC;
> > - req.mem.type = DM_IO_VMA;
> > - req.mem.ptr.vma = (char *)wc->memory_map;
> > - req.client = wc->dm_io;
> > - req.notify.fn = NULL;
> > -
> > - r = dm_io(&req, 1, ®ion, NULL);
> > + r = writecache_read_metadata(wc,
> > + min((sector_t)bdev_logical_block_size(wc->ssd_dev->bdev) >> SECTOR_SHIFT,
> > + (sector_t)wc->metadata_sectors));
>
> Can you explain why this is needed? Why isn't wc->metadata_sectors
> already compatible with wc->ssd_dev->bdev ?
bdev_logical_block_size is the minimum size accepted by the device. If we
used just bdev_logical_block_size(wc->ssd_dev->bdev), someone could (by
using extremely small device with large logical_block_size) trigger
writing out of the allocated memory.
> Yet you just use wc->metadata_sectors in the new call to
> writecache_read_metadata() in writecache_resume()...
This was my mistake. Change it to "region.count = n_sectors";
> Mike
Mikulas
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