drbd: fix NULL pointer dereference on 4k hard sect size

we still don't support 4k 'physical' sectors 'natively',
but use a read-modify-write workaround.
And we even tried to use the extra page before we allocated it :(

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 4df3b40b1057d225fe310601c77021a6f37f0d7c..d53d36cd0e5755b97499c521e3395fe1b84b6d60 100644 (file)
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -941,6 +941,25 @@ static int drbd_nl_disk_conf(struct drbd_conf *mdev, struct drbd_nl_cfg_req *nlp
 
        drbd_md_set_sector_offsets(mdev, nbc);
 
+       /* allocate a second IO page if logical_block_size != 512 */
+       logical_block_size = bdev_logical_block_size(nbc->md_bdev);
+       if (logical_block_size == 0)
+               logical_block_size = MD_SECTOR_SIZE;
+
+       if (logical_block_size != MD_SECTOR_SIZE) {
+               if (!mdev->md_io_tmpp) {
+                       struct page *page = alloc_page(GFP_NOIO);
+                       if (!page)
+                               goto force_diskless_dec;
+
+                       dev_warn(DEV, "Meta data's bdev logical_block_size = %d != %d\n",
+                            logical_block_size, MD_SECTOR_SIZE);
+                       dev_warn(DEV, "Workaround engaged (has performance impact).\n");
+
+                       mdev->md_io_tmpp = page;
+               }
+       }
+
        if (!mdev->bitmap) {
                if (drbd_bm_init(mdev)) {
                        retcode = ERR_NOMEM;
@@ -980,25 +999,6 @@ static int drbd_nl_disk_conf(struct drbd_conf *mdev, struct drbd_nl_cfg_req *nlp
                goto force_diskless_dec;
        }
 
-       /* allocate a second IO page if logical_block_size != 512 */
-       logical_block_size = bdev_logical_block_size(nbc->md_bdev);
-       if (logical_block_size == 0)
-               logical_block_size = MD_SECTOR_SIZE;
-
-       if (logical_block_size != MD_SECTOR_SIZE) {
-               if (!mdev->md_io_tmpp) {
-                       struct page *page = alloc_page(GFP_NOIO);
-                       if (!page)
-                               goto force_diskless_dec;
-
-                       dev_warn(DEV, "Meta data's bdev logical_block_size = %d != %d\n",
-                            logical_block_size, MD_SECTOR_SIZE);
-                       dev_warn(DEV, "Workaround engaged (has performance impact).\n");
-
-                       mdev->md_io_tmpp = page;
-               }
-       }
-
        /* Reset the "barriers don't work" bits here, then force meta data to
         * be written, to ensure we determine if barriers are supported. */
        if (nbc->dc.no_md_flush)