bcache: Fix for handling overlapping extents when reading in a btree node

commit 84786438ed17978d72eeced580ab757e4da8830b upstream.

btree_sort_fixup() was overly clever, because it was trying to avoid
pulling a key off the btree iterator in more than one place.

This led to a really obscure bug where we'd break early from the loop in
btree_sort_fixup() if the current key overlapped with keys in more than
one older set, and the next key it overlapped with was zero size.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 28 insertions, 11 deletions

diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index cb4578a327b9..14032e8c7731 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -918,28 +918,45 @@ struct bkey *bch_next_recurse_key(struct btree *b, struct bkey *search)
 
 /* Mergesort */
 
+static void sort_key_next(struct btree_iter *iter,
+                          struct btree_iter_set *i)
+{
+        i->k = bkey_next(i->k);
+
+        if (i->k == i->end)
+                *i = iter->data[--iter->used];
+}
+
 static void btree_sort_fixup(struct btree_iter *iter)
 {
         while (iter->used > 1) {
                 struct btree_iter_set *top = iter->data, *i = top + 1;
-                struct bkey *k;
 
                 if (iter->used > 2 &&
                     btree_iter_cmp(i[0], i[1]))
                         i++;
 
-                for (k = i->k;
-                     k != i->end && bkey_cmp(top->k, &START_KEY(k)) > 0;
-                     k = bkey_next(k))
-                        if (top->k > i->k)
-                                __bch_cut_front(top->k, k);
-                        else if (KEY_SIZE(k))
-                                bch_cut_back(&START_KEY(k), top->k);
-
-                if (top->k < i->k || k == i->k)
+                if (bkey_cmp(top->k, &START_KEY(i->k)) <= 0)
                         break;
 
-                heap_sift(iter, i - top, btree_iter_cmp);
+                if (!KEY_SIZE(i->k)) {
+                        sort_key_next(iter, i);
+                        heap_sift(iter, i - top, btree_iter_cmp);
+                        continue;
+                }
+
+                if (top->k > i->k) {
+                        if (bkey_cmp(top->k, i->k) >= 0)
+                                sort_key_next(iter, i);
+                        else
+                                bch_cut_front(top->k, i->k);
+
+                        heap_sift(iter, i - top, btree_iter_cmp);
+                } else {
+                        /* can't happen because of comparison func */
+                        BUG_ON(!bkey_cmp(&START_KEY(top->k), &START_KEY(i->k)));
+                        bch_cut_back(&START_KEY(i->k), top->k);
+                }
         }
 }