drbd: drop wrong debug asserts, fix recently introduced race

 commit 2372c38caadeaebc68a5ee190782c2a0df01edc3
 drbd: fix for possible deadlock on IO error during resync

introduced a new ASSERT, which turns out to be wrong. Drop it.

Also serialize the state change to D_DISKLESS with the after state
change work of the -> D_FAILED transition, don't open a new race.

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_main.c b/drivers/block/drbd/drbd_main.c
index f89b974..342574f 100644 (file)
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -1393,17 +1393,22 @@ static void after_state_ch(struct drbd_conf *mdev, union drbd_state os,
        }
 
        if (os.disk > D_DISKLESS && ns.disk == D_DISKLESS) {
-               int c = atomic_read(&mdev->local_cnt);
-
+               /* We must still be diskless,
+                * re-attach has to be serialized with this! */
+               if (mdev->state.disk != D_DISKLESS)
+                       dev_err(DEV,
+                               "ASSERT FAILED: disk is %s while going diskless\n",
+                               drbd_disk_str(mdev->state.disk));
+
+               /* we cannot assert local_cnt == 0 here, as get_ldev_if_state
+                * will inc/dec it frequently. Since we became D_DISKLESS, no
+                * one has touched the protected members anymore, though, so we
+                * are safe to free them here. */
                if (drbd_send_state(mdev))
                        dev_warn(DEV, "Notified peer that I detached my disk.\n");
                else
                        dev_err(DEV, "Sending state for detach failed\n");
 
-               if (c != 0) {
-                       dev_err(DEV, "Logic bug, local_cnt=%d, but should be 0\n", c);
-                       wait_event(mdev->misc_wait, !atomic_read(&mdev->local_cnt));
-               }
                lc_destroy(mdev->resync);
                mdev->resync = NULL;
                lc_destroy(mdev->act_log);
@@ -3723,8 +3728,10 @@ static int w_bitmap_io(struct drbd_conf *mdev, struct drbd_work *w, int unused)
 static int w_go_diskless(struct drbd_conf *mdev, struct drbd_work *w, int unused)
 {
        D_ASSERT(mdev->state.disk == D_FAILED);
-       D_ASSERT(atomic_read(&mdev->local_cnt) == 0);
-
+       /* we cannot assert local_cnt == 0 here, as get_ldev_if_state will
+        * inc/dec it frequently. Once we are D_DISKLESS, no one will touch
+        * the protected members anymore, though, so in the after_state_ch work
+        * it will be safe to free them. */
        drbd_force_state(mdev, NS(disk, D_DISKLESS));
 
        clear_bit(GO_DISKLESS, &mdev->flags);
@@ -3735,7 +3742,10 @@ void drbd_go_diskless(struct drbd_conf *mdev)
 {
        D_ASSERT(mdev->state.disk == D_FAILED);
        if (!test_and_set_bit(GO_DISKLESS, &mdev->flags))
-               drbd_queue_work_front(&mdev->data.work, &mdev->go_diskless);
+               drbd_queue_work(&mdev->data.work, &mdev->go_diskless);
+               /* don't drbd_queue_work_front,
+                * we need to serialize with the after_state_ch work
+                * of the -> D_FAILED transition. */
 }
 
 /**