sbitmap: check cleared bits when iterating busy bits

[Jens Axboe]

When we are iterating the set bits in a word, we also need to factor in
the cleared bits. Don't call fn() unless the bit is also not set in
the cleared word.

Fixes: ea86ea2cdced ("sbitmap: ammortize cost of clearing bits")
Signed-off-by: Jens Axboe <ax...@kernel.dk>

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 92806a2dbab7..9f374fbcdba6 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -283,6 +283,11 @@ static inline void __sbitmap_for_each_set(struct sbitmap 
*sb,
                        nr = find_next_bit(&word->word, depth, nr);
                        if (nr >= depth)
                                break;
+                       /* if set in cleared, it's actually free */
+                       if (test_bit(nr, &word->cleared)) {
+                               nr++;
+                               continue;
+                       }
                        if (!fn(sb, (index << sb->shift) + nr, data))
                                return;
 
-- 
Jens Axboe