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;