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dm btree: fix a bug in dm_btree_find_next_single()

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dm_btree_find_next_single() can short-circuit the search for a block
with a return of -ENODATA if all entries are higher than the search key
passed to lower_bound().

This hasn't been a problem because of the way the btree has been used by
DM thinp.  But it must be fixed now in preparation for fixing the race
in DM thinp's handling of simultaneous block discard vs allocation.
Otherwise, once that fix is in place, some of the blocks in a discard
would not be unmapped as expected.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Joe Thornber 2016-07-01 11:09:13 +01:00 committed by Mike Snitzer
parent 89d3d9a1e3
commit e7e0f73047
1 changed files with 8 additions and 1 deletions
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9
drivers/md/persistent-data/dm-btree.c
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@ -429,7 +429,14 @@ static int dm_btree_lookup_next_single(struct dm_btree_info *info, dm_block_t ro
if (flags & INTERNAL_NODE) {
i = lower_bound(n, key);
if (i < 0 || i >= nr_entries) {
if (i < 0) {
/*
* avoid early -ENODATA return when all entries are
* higher than the search @key.
*/
i = 0;
}
if (i >= nr_entries) {
r = -ENODATA;
goto out;
}