md: free unused memory after bitmap resize

When bitmap is resized, the old kalloced chunks just are not released
once the resized bitmap starts to use new space.

This fixes in particular kmemleak reports like this one:

unreferenced object 0xffff8f4311e9c000 (size 4096):
  comm "lvm", pid 19333, jiffies 4295263268 (age 528.265s)
  hex dump (first 32 bytes):
    02 80 02 80 02 80 02 80 02 80 02 80 02 80 02 80  ................
    02 80 02 80 02 80 02 80 02 80 02 80 02 80 02 80  ................
  backtrace:
    [<ffffffffa69471ca>] kmemleak_alloc+0x4a/0xa0
    [<ffffffffa628c10e>] kmem_cache_alloc_trace+0x14e/0x2e0
    [<ffffffffa676cfec>] bitmap_checkpage+0x7c/0x110
    [<ffffffffa676d0c5>] bitmap_get_counter+0x45/0xd0
    [<ffffffffa676d6b3>] bitmap_set_memory_bits+0x43/0xe0
    [<ffffffffa676e41c>] bitmap_init_from_disk+0x23c/0x530
    [<ffffffffa676f1ae>] bitmap_load+0xbe/0x160
    [<ffffffffc04c47d3>] raid_preresume+0x203/0x2f0 [dm_raid]
    [<ffffffffa677762f>] dm_table_resume_targets+0x4f/0xe0
    [<ffffffffa6774b52>] dm_resume+0x122/0x140
    [<ffffffffa6779b9f>] dev_suspend+0x18f/0x290
    [<ffffffffa677a3a7>] ctl_ioctl+0x287/0x560
    [<ffffffffa677a693>] dm_ctl_ioctl+0x13/0x20
    [<ffffffffa62d6b46>] do_vfs_ioctl+0xa6/0x750
    [<ffffffffa62d7269>] SyS_ioctl+0x79/0x90
    [<ffffffffa6956d41>] entry_SYSCALL_64_fastpath+0x1f/0xc2
Signed-off-by: Zdenek Kabelac <zkabelac@redhat.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/md-bitmap.c

@@ -2162,6 +2162,7 @@ int bitmap_resize(struct bitmap *bitmap, sector_t blocks,
 				for (k = 0; k < page; k++) {
 					kfree(new_bp[k].map);
 				}
+				kfree(new_bp);
 
 				/* restore some fields from old_counts */
 				bitmap->counts.bp = old_counts.bp;
@@ -2212,6 +2213,14 @@ int bitmap_resize(struct bitmap *bitmap, sector_t blocks,
 		block += old_blocks;
 	}
 
+	if (bitmap->counts.bp != old_counts.bp) {
+		unsigned long k;
+		for (k = 0; k < old_counts.pages; k++)
+			if (!old_counts.bp[k].hijacked)
+				kfree(old_counts.bp[k].map);
+		kfree(old_counts.bp);
+	}
+
 	if (!init) {
 		int i;
 		while (block < (chunks << chunkshift)) {