blk-mq: introduce BLK_STS_DEV_RESOURCE

This status is returned from driver to block layer if device related
resource is unavailable, but driver can guarantee that IO dispatch
will be triggered in future when the resource is available.

Convert some drivers to return BLK_STS_DEV_RESOURCE.  Also, if driver
returns BLK_STS_RESOURCE and SCHED_RESTART is set, rerun queue after
a delay (BLK_MQ_DELAY_QUEUE) to avoid IO stalls.  BLK_MQ_DELAY_QUEUE is
3 ms because both scsi-mq and nvmefc are using that magic value.

If a driver can make sure there is in-flight IO, it is safe to return
BLK_STS_DEV_RESOURCE because:

1) If all in-flight IOs complete before examining SCHED_RESTART in
blk_mq_dispatch_rq_list(), SCHED_RESTART must be cleared, so queue
is run immediately in this case by blk_mq_dispatch_rq_list();

2) if there is any in-flight IO after/when examining SCHED_RESTART
in blk_mq_dispatch_rq_list():
- if SCHED_RESTART isn't set, queue is run immediately as handled in 1)
- otherwise, this request will be dispatched after any in-flight IO is
  completed via blk_mq_sched_restart()

3) if SCHED_RESTART is set concurently in context because of
BLK_STS_RESOURCE, blk_mq_delay_run_hw_queue() will cover the above two
cases and make sure IO hang can be avoided.

One invariant is that queue will be rerun if SCHED_RESTART is set.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index a2005a485335b5b42082bf02ffd7b3d1e90b3f3c..134fd34b681f0a9a6a2b0b666fa6c8c0e84380eb 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -145,6 +145,7 @@ static const struct {
        [BLK_STS_MEDIUM]        = { -ENODATA,   "critical medium" },
        [BLK_STS_PROTECTION]    = { -EILSEQ,    "protection" },
        [BLK_STS_RESOURCE]      = { -ENOMEM,    "kernel resource" },
+       [BLK_STS_DEV_RESOURCE]  = { -EBUSY,     "device resource" },
        [BLK_STS_AGAIN]         = { -EAGAIN,    "nonblocking retry" },
 
        /* device mapper special case, should not leak out: */

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 01f271d40825ebfd6ca82fdd2f887d432946799c..df93102e21494dc7f98456e4376ce7c83fca56ab 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1162,6 +1162,8 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx **hctx,
        return true;
 }
 
+#define BLK_MQ_RESOURCE_DELAY  3               /* ms units */
+
 bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
                             bool got_budget)
 {
@@ -1169,6 +1171,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
        struct request *rq, *nxt;
        bool no_tag = false;
        int errors, queued;
+       blk_status_t ret = BLK_STS_OK;
 
        if (list_empty(list))
                return false;
@@ -1181,7 +1184,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
        errors = queued = 0;
        do {
                struct blk_mq_queue_data bd;
-               blk_status_t ret;
 
                rq = list_first_entry(list, struct request, queuelist);
                if (!blk_mq_get_driver_tag(rq, &hctx, false)) {
@@ -1226,7 +1228,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
                }
 
                ret = q->mq_ops->queue_rq(hctx, &bd);
-               if (ret == BLK_STS_RESOURCE) {
+               if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {
                        /*
                         * If an I/O scheduler has been configured and we got a
                         * driver tag for the next request already, free it
@@ -1257,6 +1259,8 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
         * that is where we will continue on next queue run.
         */
        if (!list_empty(list)) {
+               bool needs_restart;
+
                spin_lock(&hctx->lock);
                list_splice_init(list, &hctx->dispatch);
                spin_unlock(&hctx->lock);
@@ -1280,10 +1284,17 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
                 * - Some but not all block drivers stop a queue before
                 *   returning BLK_STS_RESOURCE. Two exceptions are scsi-mq
                 *   and dm-rq.
+                *
+                * If driver returns BLK_STS_RESOURCE and SCHED_RESTART
+                * bit is set, run queue after a delay to avoid IO stalls
+                * that could otherwise occur if the queue is idle.
                 */
-               if (!blk_mq_sched_needs_restart(hctx) ||
+               needs_restart = blk_mq_sched_needs_restart(hctx);
+               if (!needs_restart ||
                    (no_tag && list_empty_careful(&hctx->dispatch_wait.entry)))
                        blk_mq_run_hw_queue(hctx, true);
+               else if (needs_restart && (ret == BLK_STS_RESOURCE))
+                       blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);
        }
 
        return (queued + errors) != 0;
@@ -1764,6 +1775,7 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
                *cookie = new_cookie;
                break;
        case BLK_STS_RESOURCE:
+       case BLK_STS_DEV_RESOURCE:
                __blk_mq_requeue_request(rq);
                break;
        default:
@@ -1826,7 +1838,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
        hctx_lock(hctx, &srcu_idx);
 
        ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false);
-       if (ret == BLK_STS_RESOURCE)
+       if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
                blk_mq_sched_insert_request(rq, false, true, false);
        else if (ret != BLK_STS_OK)
                blk_mq_end_request(rq, ret);

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 6655893a3a7a8365a5feb4f035b65021d38f3847..287a09611c0f8addd756c41d4733b6773f25badc 100644 (file)
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -1230,7 +1230,7 @@ static blk_status_t null_handle_cmd(struct nullb_cmd *cmd)
                                return BLK_STS_OK;
                        } else
                                /* requeue request */
-                               return BLK_STS_RESOURCE;
+                               return BLK_STS_DEV_RESOURCE;
                }
        }
 

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 68846897d2139baa1208619469a4ef15385d7aa8..79908e6ddbf2605d2a0ee67e721ffd6048e75aa7 100644 (file)
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -276,7 +276,7 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
                /* Out of mem doesn't actually happen, since we fall back
                 * to direct descriptors */
                if (err == -ENOMEM || err == -ENOSPC)
-                       return BLK_STS_RESOURCE;
+                       return BLK_STS_DEV_RESOURCE;
                return BLK_STS_IOERR;
        }
 

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 891265acb10ec3c0af6a2ddc9e76c14ccc70cfb2..e126e4cac2ca499566da91a6e3da01d0b1e4381e 100644 (file)
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -911,7 +911,7 @@ out_err:
 out_busy:
        blk_mq_stop_hw_queue(hctx);
        spin_unlock_irqrestore(&rinfo->ring_lock, flags);
-       return BLK_STS_RESOURCE;
+       return BLK_STS_DEV_RESOURCE;
 }
 
 static void blkif_complete_rq(struct request *rq)

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index b7d175e94a0233312e63b70678f4db7a57f6b9be..348a0cb6963a8012647114e06803283422644ef6 100644 (file)
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -404,7 +404,7 @@ static blk_status_t dm_dispatch_clone_request(struct request *clone, struct requ
 
        clone->start_time = jiffies;
        r = blk_insert_cloned_request(clone->q, clone);
-       if (r != BLK_STS_OK && r != BLK_STS_RESOURCE)
+       if (r != BLK_STS_OK && r != BLK_STS_RESOURCE && r != BLK_STS_DEV_RESOURCE)
                /* must complete clone in terms of original request */
                dm_complete_request(rq, r);
        return r;
@@ -496,7 +496,7 @@ check_again:
                trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)),
                                     blk_rq_pos(rq));
                ret = dm_dispatch_clone_request(clone, rq);
-               if (ret == BLK_STS_RESOURCE) {
+               if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {
                        blk_rq_unprep_clone(clone);
                        tio->ti->type->release_clone_rq(clone);
                        tio->clone = NULL;
@@ -769,7 +769,6 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
                /* Undo dm_start_request() before requeuing */
                rq_end_stats(md, rq);
                rq_completed(md, rq_data_dir(rq), false);
-               blk_mq_delay_run_hw_queue(hctx, 100/*ms*/);
                return BLK_STS_RESOURCE;
        }
 

diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
index 99bf51c7e51325e25ead4f4bb0dfbeff7972e526..b856d7c919d298062e2e55d8495ca18891d4f0f2 100644 (file)
--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -35,8 +35,6 @@ enum nvme_fc_queue_flags {
        NVME_FC_Q_LIVE,
 };
 
-#define NVMEFC_QUEUE_DELAY     3               /* ms units */
-
 #define NVME_FC_DEFAULT_DEV_LOSS_TMO   60      /* seconds */
 
 struct nvme_fc_queue {
@@ -2231,7 +2229,7 @@ nvme_fc_start_fcp_op(struct nvme_fc_ctrl *ctrl, struct nvme_fc_queue *queue,
         * the target device is present
         */
        if (ctrl->rport->remoteport.port_state != FC_OBJSTATE_ONLINE)
-               goto busy;
+               return BLK_STS_RESOURCE;
 
        if (!nvme_fc_ctrl_get(ctrl))
                return BLK_STS_IOERR;
@@ -2311,16 +2309,10 @@ nvme_fc_start_fcp_op(struct nvme_fc_ctrl *ctrl, struct nvme_fc_queue *queue,
                                ret != -EBUSY)
                        return BLK_STS_IOERR;
 
-               goto busy;
+               return BLK_STS_RESOURCE;
        }
 
        return BLK_STS_OK;
-
-busy:
-       if (!(op->flags & FCOP_FLAGS_AEN) && queue->hctx)
-               blk_mq_delay_run_hw_queue(queue->hctx, NVMEFC_QUEUE_DELAY);
-
-       return BLK_STS_RESOURCE;
 }
 
 static inline blk_status_t nvme_fc_is_ready(struct nvme_fc_queue *queue,

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d9ca1dfab154c83f79ba1dab210f1a3521d1ea5d..55be2550c555b3b910c63b3b7ca623b8abf9a98d 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2030,9 +2030,9 @@ out_put_budget:
        case BLK_STS_OK:
                break;
        case BLK_STS_RESOURCE:
-               if (atomic_read(&sdev->device_busy) == 0 &&
-                   !scsi_device_blocked(sdev))
-                       blk_mq_delay_run_hw_queue(hctx, SCSI_QUEUE_DELAY);
+               if (atomic_read(&sdev->device_busy) ||
+                   scsi_device_blocked(sdev))
+                       ret = BLK_STS_DEV_RESOURCE;
                break;
        default:
                /*

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index c5d3db0d83f8ac1adf177f0f92c7bf3ed0e2c261..bf18b95ed92d566466709b95d826fa64fb640fb8 100644 (file)
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -39,6 +39,24 @@ typedef u8 __bitwise blk_status_t;
 
 #define BLK_STS_AGAIN          ((__force blk_status_t)12)
 
+/*
+ * BLK_STS_DEV_RESOURCE is returned from the driver to the block layer if
+ * device related resources are unavailable, but the driver can guarantee
+ * that the queue will be rerun in the future once resources become
+ * available again. This is typically the case for device specific
+ * resources that are consumed for IO. If the driver fails allocating these
+ * resources, we know that inflight (or pending) IO will free these
+ * resource upon completion.
+ *
+ * This is different from BLK_STS_RESOURCE in that it explicitly references
+ * a device specific resource. For resources of wider scope, allocation
+ * failure can happen without having pending IO. This means that we can't
+ * rely on request completions freeing these resources, as IO may not be in
+ * flight. Examples of that are kernel memory allocations, DMA mappings, or
+ * any other system wide resources.
+ */
+#define BLK_STS_DEV_RESOURCE   ((__force blk_status_t)13)
+
 /**
  * blk_path_error - returns true if error may be path related
  * @error: status the request was completed with