umem: fix up unplugging

Fix a regression introduced by 7eaceaccab5f40 ("block: remove per-queue
plugging").  In that patch, Jens removed the whole mm_unplug_device()
function, which used to be the trigger to make umem start to work.

We need to implement unplugging to make umem start to work, or I/O will
never be triggered.

Signed-off-by: Tao Guo <Tao.Guo@emc.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Shaohua Li <shli@kernel.org>
Cc: <stable@vger.kernel.org>
Acked-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 40 insertions, 0 deletions

diff --git a/drivers/block/umem.c b/drivers/block/umem.c
index aa2712060bf..9a72277a31d 100644
--- a/drivers/block/umem.c
+++ b/drivers/block/umem.c
@@ -513,6 +513,44 @@ static void process_page(unsigned long data)
         }
 }
 
+struct mm_plug_cb {
+        struct blk_plug_cb cb;
+        struct cardinfo *card;
+};
+
+static void mm_unplug(struct blk_plug_cb *cb)
+{
+        struct mm_plug_cb *mmcb = container_of(cb, struct mm_plug_cb, cb);
+
+        spin_lock_irq(&mmcb->card->lock);
+        activate(mmcb->card);
+        spin_unlock_irq(&mmcb->card->lock);
+        kfree(mmcb);
+}
+
+static int mm_check_plugged(struct cardinfo *card)
+{
+        struct blk_plug *plug = current->plug;
+        struct mm_plug_cb *mmcb;
+
+        if (!plug)
+                return 0;
+
+        list_for_each_entry(mmcb, &plug->cb_list, cb.list) {
+                if (mmcb->cb.callback == mm_unplug && mmcb->card == card)
+                        return 1;
+        }
+        /* Not currently on the callback list */
+        mmcb = kmalloc(sizeof(*mmcb), GFP_ATOMIC);
+        if (!mmcb)
+                return 0;
+
+        mmcb->card = card;
+        mmcb->cb.callback = mm_unplug;
+        list_add(&mmcb->cb.list, &plug->cb_list);
+        return 1;
+}
+
 static void mm_make_request(struct request_queue *q, struct bio *bio)
 {
         struct cardinfo *card = q->queuedata;
@@ -523,6 +561,8 @@ static void mm_make_request(struct request_queue *q, struct bio *bio)
         *card->biotail = bio;
         bio->bi_next = NULL;
         card->biotail = &bio->bi_next;
+        if (bio->bi_rw & REQ_SYNC || !mm_check_plugged(card))
+                activate(card);
         spin_unlock_irq(&card->lock);
 
         return;