diff options
Diffstat (limited to 'drivers/scsi/virtio_scsi.c')
| -rw-r--r-- | drivers/scsi/virtio_scsi.c | 78 |
1 files changed, 13 insertions, 65 deletions
diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c index db3b494e5926..d4727b339474 100644 --- a/drivers/scsi/virtio_scsi.c +++ b/drivers/scsi/virtio_scsi.c @@ -73,17 +73,12 @@ struct virtio_scsi_vq { * queue, and also lets the driver optimize the IRQ affinity for the virtqueues * (each virtqueue's affinity is set to the CPU that "owns" the queue). * - * An interesting effect of this policy is that only writes to req_vq need to - * take the tgt_lock. Read can be done outside the lock because: + * tgt_lock is held to serialize reading and writing req_vq. Reading req_vq + * could be done locklessly, but we do not do it yet. * - * - writes of req_vq only occur when atomic_inc_return(&tgt->reqs) returns 1. - * In that case, no other CPU is reading req_vq: even if they were in - * virtscsi_queuecommand_multi, they would be spinning on tgt_lock. - * - * - reads of req_vq only occur when the target is not idle (reqs != 0). - * A CPU that enters virtscsi_queuecommand_multi will not modify req_vq. - * - * Similarly, decrements of reqs are never concurrent with writes of req_vq. + * Decrements of reqs are never concurrent with writes of req_vq: before the + * decrement reqs will be != 0; after the decrement the virtqueue completion + * routine will not use the req_vq so it can be changed by a new request. * Thus they can happen outside the tgt_lock, provided of course we make reqs * an atomic_t. */ @@ -204,7 +199,6 @@ static void virtscsi_complete_cmd(struct virtio_scsi *vscsi, void *buf) set_driver_byte(sc, DRIVER_SENSE); } - mempool_free(cmd, virtscsi_cmd_pool); sc->scsi_done(sc); atomic_dec(&tgt->reqs); @@ -238,38 +232,6 @@ static void virtscsi_req_done(struct virtqueue *vq) int index = vq->index - VIRTIO_SCSI_VQ_BASE; struct virtio_scsi_vq *req_vq = &vscsi->req_vqs[index]; - /* - * Read req_vq before decrementing the reqs field in - * virtscsi_complete_cmd. - * - * With barriers: - * - * CPU #0 virtscsi_queuecommand_multi (CPU #1) - * ------------------------------------------------------------ - * lock vq_lock - * read req_vq - * read reqs (reqs = 1) - * write reqs (reqs = 0) - * increment reqs (reqs = 1) - * write req_vq - * - * Possible reordering without barriers: - * - * CPU #0 virtscsi_queuecommand_multi (CPU #1) - * ------------------------------------------------------------ - * lock vq_lock - * read reqs (reqs = 1) - * write reqs (reqs = 0) - * increment reqs (reqs = 1) - * write req_vq - * read (wrong) req_vq - * - * We do not need a full smp_rmb, because req_vq is required to get - * to tgt->reqs: tgt is &vscsi->tgt[sc->device->id], where sc is stored - * in the virtqueue as the user token. - */ - smp_read_barrier_depends(); - virtscsi_vq_done(vscsi, req_vq, virtscsi_complete_cmd); }; @@ -279,8 +241,6 @@ static void virtscsi_complete_free(struct virtio_scsi *vscsi, void *buf) if (cmd->comp) complete_all(cmd->comp); - else - mempool_free(cmd, virtscsi_cmd_pool); } static void virtscsi_ctrl_done(struct virtqueue *vq) @@ -496,10 +456,9 @@ static int virtscsi_queuecommand(struct virtio_scsi *vscsi, struct virtio_scsi_vq *req_vq, struct scsi_cmnd *sc) { - struct virtio_scsi_cmd *cmd; - int ret; - struct Scsi_Host *shost = virtio_scsi_host(vscsi->vdev); + struct virtio_scsi_cmd *cmd = scsi_cmd_priv(sc); + BUG_ON(scsi_sg_count(sc) > shost->sg_tablesize); /* TODO: check feature bit and fail if unsupported? */ @@ -508,11 +467,6 @@ static int virtscsi_queuecommand(struct virtio_scsi *vscsi, dev_dbg(&sc->device->sdev_gendev, "cmd %p CDB: %#02x\n", sc, sc->cmnd[0]); - ret = SCSI_MLQUEUE_HOST_BUSY; - cmd = mempool_alloc(virtscsi_cmd_pool, GFP_ATOMIC); - if (!cmd) - goto out; - memset(cmd, 0, sizeof(*cmd)); cmd->sc = sc; cmd->req.cmd = (struct virtio_scsi_cmd_req){ @@ -531,13 +485,9 @@ static int virtscsi_queuecommand(struct virtio_scsi *vscsi, if (virtscsi_kick_cmd(req_vq, cmd, sizeof cmd->req.cmd, sizeof cmd->resp.cmd, - GFP_ATOMIC) == 0) - ret = 0; - else - mempool_free(cmd, virtscsi_cmd_pool); - -out: - return ret; + GFP_ATOMIC) != 0) + return SCSI_MLQUEUE_HOST_BUSY; + return 0; } static int virtscsi_queuecommand_single(struct Scsi_Host *sh, @@ -560,12 +510,8 @@ static struct virtio_scsi_vq *virtscsi_pick_vq(struct virtio_scsi *vscsi, spin_lock_irqsave(&tgt->tgt_lock, flags); - /* - * The memory barrier after atomic_inc_return matches - * the smp_read_barrier_depends() in virtscsi_req_done. - */ if (atomic_inc_return(&tgt->reqs) > 1) - vq = ACCESS_ONCE(tgt->req_vq); + vq = tgt->req_vq; else { queue_num = smp_processor_id(); while (unlikely(queue_num >= vscsi->num_queues)) @@ -683,6 +629,7 @@ static struct scsi_host_template virtscsi_host_template_single = { .name = "Virtio SCSI HBA", .proc_name = "virtio_scsi", .this_id = -1, + .cmd_size = sizeof(struct virtio_scsi_cmd), .queuecommand = virtscsi_queuecommand_single, .eh_abort_handler = virtscsi_abort, .eh_device_reset_handler = virtscsi_device_reset, @@ -699,6 +646,7 @@ static struct scsi_host_template virtscsi_host_template_multi = { .name = "Virtio SCSI HBA", .proc_name = "virtio_scsi", .this_id = -1, + .cmd_size = sizeof(struct virtio_scsi_cmd), .queuecommand = virtscsi_queuecommand_multi, .eh_abort_handler = virtscsi_abort, .eh_device_reset_handler = virtscsi_device_reset, |