drbd: fix potential deadlock during bitmap (re-)allocation

The former comment arguing that GFP_KERNEL was good enough was wrong: it
did not take resize into account at all, and assumed the only path
leading here was the normal attach on a still secondary device, so no
deadlock would be possible.

Both resize on a Primary, or attach on a diskless Primary,
could potentially deadlock.

drbd_bm_resize() is called while IO to the respective device is
suspended, so we must use GFP_NOIO to avoid potential deadlock.

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

1 files changed, 9 insertions, 7 deletions

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index 4a076b2553e6..e502535d2c4d 100644
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -388,14 +388,16 @@ static struct page **bm_realloc_pages(struct drbd_bitmap *b, unsigned long want)
                 return old_pages;
 
         /* Trying kmalloc first, falling back to vmalloc.
-         * GFP_KERNEL is ok, as this is done when a lower level disk is
-         * "attached" to the drbd.  Context is receiver thread or drbdsetup /
-         * netlink process.  As we have no disk yet, we are not in the IO path,
-         * not even the IO path of the peer. */
+         * GFP_NOIO, as this is called while drbd IO is "suspended",
+         * and during resize or attach on diskless Primary,
+         * we must not block on IO to ourselves.
+         * Context is receiver thread or dmsetup. */
         bytes = sizeof(struct page *)*want;
-        new_pages = kmalloc(bytes, GFP_KERNEL);
+        new_pages = kmalloc(bytes, GFP_NOIO);
         if (!new_pages) {
-                new_pages = vmalloc(bytes);
+                new_pages = __vmalloc(bytes,
+                                GFP_NOIO | __GFP_HIGHMEM,
+                                PAGE_KERNEL);
                 if (!new_pages)
                         return NULL;
                 vmalloced = 1;
@@ -406,7 +408,7 @@ static struct page **bm_realloc_pages(struct drbd_bitmap *b, unsigned long want)
                 for (i = 0; i < have; i++)
                         new_pages[i] = old_pages[i];
                 for (; i < want; i++) {
-                        page = alloc_page(GFP_HIGHUSER);
+                        page = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
                         if (!page) {
                                 bm_free_pages(new_pages + have, i - have);
                                 bm_vk_free(new_pages, vmalloced);