block: loop: convert to per-device workqueue

Documentation/workqueue.txt:
	If there is dependency among multiple work items used
	during memory reclaim, they should be queued to separate
	wq each with WQ_MEM_RECLAIM.

Loop devices can be stacked, so we have to convert to per-device
workqueue. One example is Fedora live CD.

Fixes: b5dd2f6047ca108001328aac0e8588edd15f1778
Cc: stable@vger.kernel.org (v4.0)
Cc: Justin M. Forbes <jforbes@fedoraproject.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ae3fcb4..3dc1598 100644 (file)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -86,8 +86,6 @@ static DEFINE_MUTEX(loop_index_mutex);
 static int max_part;
 static int part_shift;
 
-static struct workqueue_struct *loop_wq;
-
 static int transfer_xor(struct loop_device *lo, int cmd,
                        struct page *raw_page, unsigned raw_off,
                        struct page *loop_page, unsigned loop_off,
@@ -725,6 +723,12 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
        size = get_loop_size(lo, file);
        if ((loff_t)(sector_t)size != size)
                goto out_putf;
+       error = -ENOMEM;
+       lo->wq = alloc_workqueue("kloopd%d",
+                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0,
+                       lo->lo_number);
+       if (!lo->wq)
+               goto out_putf;
 
        error = 0;
 
@@ -872,6 +876,8 @@ static int loop_clr_fd(struct loop_device *lo)
        lo->lo_flags = 0;
        if (!part_shift)
                lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
+       destroy_workqueue(lo->wq);
+       lo->wq = NULL;
        mutex_unlock(&lo->lo_ctl_mutex);
        /*
         * Need not hold lo_ctl_mutex to fput backing file.
@@ -1425,9 +1431,13 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
                const struct blk_mq_queue_data *bd)
 {
        struct loop_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
+       struct loop_device *lo = cmd->rq->q->queuedata;
 
        blk_mq_start_request(bd->rq);
 
+       if (lo->lo_state != Lo_bound)
+               return -EIO;
+
        if (cmd->rq->cmd_flags & REQ_WRITE) {
                struct loop_device *lo = cmd->rq->q->queuedata;
                bool need_sched = true;
@@ -1441,9 +1451,9 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
                spin_unlock_irq(&lo->lo_lock);
 
                if (need_sched)
-                       queue_work(loop_wq, &lo->write_work);
+                       queue_work(lo->wq, &lo->write_work);
        } else {
-               queue_work(loop_wq, &cmd->read_work);
+               queue_work(lo->wq, &cmd->read_work);
        }
 
        return BLK_MQ_RQ_QUEUE_OK;
@@ -1455,9 +1465,6 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
        struct loop_device *lo = cmd->rq->q->queuedata;
        int ret = -EIO;
 
-       if (lo->lo_state != Lo_bound)
-               goto failed;
-
        if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY))
                goto failed;
 
@@ -1806,13 +1813,6 @@ static int __init loop_init(void)
                goto misc_out;
        }
 
-       loop_wq = alloc_workqueue("kloopd",
-                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0);
-       if (!loop_wq) {
-               err = -ENOMEM;
-               goto misc_out;
-       }
-
        blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
                                  THIS_MODULE, loop_probe, NULL, NULL);
 
@@ -1850,8 +1850,6 @@ static void __exit loop_exit(void)
        blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
        unregister_blkdev(LOOP_MAJOR, "loop");
 
-       destroy_workqueue(loop_wq);
-
        misc_deregister(&loop_misc);
 }
 

diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 301c27f..49564ed 100644 (file)
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -54,6 +54,7 @@ struct loop_device {
        gfp_t           old_gfp_mask;
 
        spinlock_t              lo_lock;
+       struct workqueue_struct *wq;
        struct list_head        write_cmd_head;
        struct work_struct      write_work;
        bool                    write_started;