virtio-mem: fix sleeping in RCU read side section in virtio_mem_online_page_cb()

virtio_mem_set_fake_offline() might sleep now, and we call it under
rcu_read_lock(). To fix it, simply move the rcu_read_unlock() further
up, as we're done with the device.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 6cc26d77613a: "virtio-mem: use page_offline_(start|end) when setting PageOffline()
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 09ed55de07d7d4f25f4d26e35b6a1d1a6f04e3fc..b91bc810a87e166a79a1808f37794b1a94499c4c 100644 (file)
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -1242,12 +1242,19 @@ static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
                        do_online = virtio_mem_bbm_get_bb_state(vm, id) !=
                                    VIRTIO_MEM_BBM_BB_FAKE_OFFLINE;
                }
+
+               /*
+                * virtio_mem_set_fake_offline() might sleep, we don't need
+                * the device anymore. See virtio_mem_remove() how races
+                * between memory onlining and device removal are handled.
+                */
+               rcu_read_unlock();
+
                if (do_online)
                        generic_online_page(page, order);
                else
                        virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order,
                                                    false);
-               rcu_read_unlock();
                return;
        }
        rcu_read_unlock();