drbd: report congestion if we are waiting for some userland callback

If the drbd worker thread is synchronously waiting for some userland
callback, we don't want some casual pageout to block on us.
Have drbd_congested() report congestion in that case.

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_int.h b/drivers/block/drbd/drbd_int.h
index 79c69ebb0653eee884f91216026c16b975d960ed..5136510ec8be139c9acd198d19a5e190a2ea0039 100644 (file)
--- 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 5bebe8d8ace31d3c613b529e80913ad4be4f6400..41ccb580d5ac81d311d102414439a4e1b66d70af 100644 (file)
--- 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 40a1c4f07190004488a2f2b4e172a4a933f7c11d..03fc853be2b91a1e7b70d266df3d2ceda1f5771b 100644 (file)
--- 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;