+
+ /*
+ * If we have a file range that points to a compressed extent
+ * and it's followed by a consecutive file range that points to
+ * to the same compressed extent (possibly with a different
+ * offset and/or length, so it either points to the whole extent
+ * or only part of it), we must make sure we do not submit a
+ * single bio to populate the pages for the 2 ranges because
+ * this makes the compressed extent read zero out the pages
+ * belonging to the 2nd range. Imagine the following scenario:
+ *
+ * File layout
+ * [0 - 8K] [8K - 24K]
+ * | |
+ * | |
+ * points to extent X, points to extent X,
+ * offset 4K, length of 8K offset 0, length 16K
+ *
+ * [extent X, compressed length = 4K uncompressed length = 16K]
+ *
+ * If the bio to read the compressed extent covers both ranges,
+ * it will decompress extent X into the pages belonging to the
+ * first range and then it will stop, zeroing out the remaining
+ * pages that belong to the other range that points to extent X.
+ * So here we make sure we submit 2 bios, one for the first
+ * range and another one for the third range. Both will target
+ * the same physical extent from disk, but we can't currently
+ * make the compressed bio endio callback populate the pages
+ * for both ranges because each compressed bio is tightly
+ * coupled with a single extent map, and each range can have
+ * an extent map with a different offset value relative to the
+ * uncompressed data of our extent and different lengths. This
+ * is a corner case so we prioritize correctness over
+ * non-optimal behavior (submitting 2 bios for the same extent).
+ */
+ if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) &&
+ prev_em_start && *prev_em_start != (u64)-1 &&
+ *prev_em_start != em->orig_start)
+ force_bio_submit = true;
+
+ if (prev_em_start)
+ *prev_em_start = em->orig_start;
+