3 files changed, 29 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 79c69ebb0653..5136510ec8be 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -850,6 +850,13 @@ enum {
         AL_SUSPENDED,           /* Activity logging is currently suspended. */
         AHEAD_TO_SYNC_SOURCE,   /* Ahead -> SyncSource queued */
         STATE_SENT,             /* Do not change state/UUIDs while this is set */
+
+        CALLBACK_PENDING,       /* Whether we have a call_usermodehelper(, UMH_WAIT_PROC)
+                                 * pending, from drbd worker context.
+                                 * If set, bdi_write_congested() returns true,
+                                 * so shrink_page_list() would not recurse into,
+                                 * and potentially deadlock on, this drbd worker.
+                                 */
 };
 
 struct drbd_bitmap; /* opaque for drbd_conf */
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 5bebe8d8ace3..41ccb580d5ac 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -3553,6 +3553,22 @@ static int drbd_congested(void *congested_data, int bdi_bits)
                 goto out;
         }
 
+        if (test_bit(CALLBACK_PENDING, &mdev->flags)) {
+                r |= (1 << BDI_async_congested);
+                /* Without good local data, we would need to read from remote,
+                 * and that would need the worker thread as well, which is
+                 * currently blocked waiting for that usermode helper to
+                 * finish.
+                 */
+                if (!get_ldev_if_state(mdev, D_UP_TO_DATE))
+                        r |= (1 << BDI_sync_congested);
+                else
+                        put_ldev(mdev);
+                r &= bdi_bits;
+                reason = 'c';
+                goto out;
+        }
+
         if (get_ldev(mdev)) {
                 q = bdev_get_queue(mdev->ldev->backing_bdev);
                 r = bdi_congested(&q->backing_dev_info, bdi_bits);
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 40a1c4f07190..03fc853be2b9 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -147,6 +147,9 @@ int drbd_khelper(struct drbd_conf *mdev, char *cmd)
         char *argv[] = {usermode_helper, cmd, mb, NULL };
         int ret;
 
+        if (current == mdev->worker.task)
+                set_bit(CALLBACK_PENDING, &mdev->flags);
+
         snprintf(mb, 12, "minor-%d", mdev_to_minor(mdev));
 
         if (get_net_conf(mdev)) {
@@ -189,6 +192,9 @@ int drbd_khelper(struct drbd_conf *mdev, char *cmd)
                                 usermode_helper, cmd, mb,
                                 (ret >> 8) & 0xff, ret);
 
+        if (current == mdev->worker.task)
+                clear_bit(CALLBACK_PENDING, &mdev->flags);
+
         if (ret < 0) /* Ignore any ERRNOs we got. */
                 ret = 0;