drbd: fix access of unallocated pages and kernel panic

[mirror_ubuntu-bionic-kernel.git] / drivers / block / drbd / drbd_bitmap.c

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index b5c5ff53cb57f74e89cc59bad8ca6e29df5e1db5..fcb956bb4b4c525875f961e7c2398b20c35723f4 100644 (file)
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -1475,10 +1475,17 @@ void _drbd_bm_set_bits(struct drbd_conf *mdev, const unsigned long s, const unsi
                first_word = 0;
                spin_lock_irq(&b->bm_lock);
        }
-
        /* last page (respectively only page, for first page == last page) */
        last_word = MLPP(el >> LN2_BPL);
-       bm_set_full_words_within_one_page(mdev->bitmap, last_page, first_word, last_word);
+
+       /* consider bitmap->bm_bits = 32768, bitmap->bm_number_of_pages = 1. (or multiples).
+        * ==> e = 32767, el = 32768, last_page = 2,
+        * and now last_word = 0.
+        * We do not want to touch last_page in this case,
+        * as we did not allocate it, it is not present in bitmap->bm_pages.
+        */
+       if (last_word)
+               bm_set_full_words_within_one_page(mdev->bitmap, last_page, first_word, last_word);
 
        /* possibly trailing bits.
         * example: (e & 63) == 63, el will be e+1.