Re: [PATCH v2] nvmet-fc: associations list protected by rcu, instead of spinlock_irq where possible.

Christoph Hellwig
2021-01-11T08:12:36Z

James, can you review this patch?

On Sun, Jan 03, 2021 at 08:12:53PM +0200, leonid.ravich@dell.com wrote:
> From: Leonid Ravich <Leonid.Ravich@emc.com>
>
> searching assoc_list protected by rcu_read_lock if list not changed inline.
> and according to the rcu list rules.
>
> queue array embedded into nvmet_fc_tgt_assoc protected by rcu_read_lock
> according to rcu dereference/assign rules.
>
> queue and assoc object freed after grace period by call_rcu.
>
> tgtport lock taken for changing assoc_list.
>
> Reviewed-by: Eldad Zinger <Eldad.Zinger@dell.com>
> Reviewed-by: Elad Grupi <Elad.Grupi@dell.com>
> Signed-off-by: Leonid Ravich <Leonid.Ravich@emc.com>
> ---
> 1) fixed sytle issus
> 2) queues array protects by rcu as well
>
> drivers/nvme/target/fc.c | 81 +++++++++++++++++++++++-------------------------
> 1 file changed, 38 insertions(+), 43 deletions(-)
>
> diff --git a/drivers/nvme/target/fc.c b/drivers/nvme/target/fc.c
> index cd4e73a..c14c60b 100644
> --- a/drivers/nvme/target/fc.c
> +++ b/drivers/nvme/target/fc.c
> @@ -145,6 +145,7 @@ struct nvmet_fc_tgt_queue {
> struct list_head avail_defer_list;
> struct workqueue_struct *work_q;
> struct kref ref;
> + struct rcu_head rcu;
> struct nvmet_fc_fcp_iod fod[]; /* array of fcp_iods */
> } __aligned(sizeof(unsigned long long));
>
> @@ -167,6 +168,7 @@ struct nvmet_fc_tgt_assoc {
> struct nvmet_fc_tgt_queue *queues[NVMET_NR_QUEUES + 1];
> struct kref ref;
> struct work_struct del_work;
> + struct rcu_head rcu;
> };
>
>
> @@ -790,7 +792,6 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> u16 qid, u16 sqsize)
> {
> struct nvmet_fc_tgt_queue *queue;
> - unsigned long flags;
> int ret;
>
> if (qid > NVMET_NR_QUEUES)
> @@ -829,9 +830,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> goto out_fail_iodlist;
>
> WARN_ON(assoc->queues[qid]);
> - spin_lock_irqsave(&assoc->tgtport->lock, flags);
> - assoc->queues[qid] = queue;
> - spin_unlock_irqrestore(&assoc->tgtport->lock, flags);
> + rcu_assign_pointer(assoc->queues[qid], queue);
>
> return queue;
>
> @@ -851,11 +850,8 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> {
> struct nvmet_fc_tgt_queue *queue =
> container_of(ref, struct nvmet_fc_tgt_queue, ref);
> - unsigned long flags;
>
> - spin_lock_irqsave(&queue->assoc->tgtport->lock, flags);
> - queue->assoc->queues[queue->qid] = NULL;
> - spin_unlock_irqrestore(&queue->assoc->tgtport->lock, flags);
> + rcu_assign_pointer(queue->assoc->queues[queue->qid], NULL);
>
> nvmet_fc_destroy_fcp_iodlist(queue->assoc->tgtport, queue);
>
> @@ -863,7 +859,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>
> destroy_workqueue(queue->work_q);
>
> - kfree(queue);
> + kfree_rcu(queue, rcu);
> }
>
> static void
> @@ -965,24 +961,23 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> struct nvmet_fc_tgt_queue *queue;
> u64 association_id = nvmet_fc_getassociationid(connection_id);
> u16 qid = nvmet_fc_getqueueid(connection_id);
> - unsigned long flags;
>
> if (qid > NVMET_NR_QUEUES)
> return NULL;
>
> - spin_lock_irqsave(&tgtport->lock, flags);
> - list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
> + rcu_read_lock();
> + list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
> if (association_id == assoc->association_id) {
> - queue = assoc->queues[qid];
> + queue = rcu_dereference(assoc->queues[qid]);
> if (queue &&
> (!atomic_read(&queue->connected) ||
> !nvmet_fc_tgt_q_get(queue)))
> queue = NULL;
> - spin_unlock_irqrestore(&tgtport->lock, flags);
> + rcu_read_unlock();
> return queue;
> }
> }
> - spin_unlock_irqrestore(&tgtport->lock, flags);
> + rcu_read_unlock();
> return NULL;
> }
>
> @@ -1137,7 +1132,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> }
> if (!needrandom) {
> assoc->association_id = ran;
> - list_add_tail(&assoc->a_list, &tgtport->assoc_list);
> + list_add_tail_rcu(&assoc->a_list, &tgtport->assoc_list);
> }
> spin_unlock_irqrestore(&tgtport->lock, flags);
> }
> @@ -1167,7 +1162,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>
> nvmet_fc_free_hostport(assoc->hostport);
> spin_lock_irqsave(&tgtport->lock, flags);
> - list_del(&assoc->a_list);
> + list_del_rcu(&assoc->a_list);
> oldls = assoc->rcv_disconn;
> spin_unlock_irqrestore(&tgtport->lock, flags);
> /* if pending Rcv Disconnect Association LS, send rsp now */
> @@ -1177,7 +1172,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> dev_info(tgtport->dev,
> "{%d:%d} Association freed\n",
> tgtport->fc_target_port.port_num, assoc->a_id);
> - kfree(assoc);
> + kfree_rcu(assoc, rcu);
> nvmet_fc_tgtport_put(tgtport);
> }
>
> @@ -1198,7 +1193,6 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> {
> struct nvmet_fc_tgtport *tgtport = assoc->tgtport;
> struct nvmet_fc_tgt_queue *queue;
> - unsigned long flags;
> int i, terminating;
>
> terminating = atomic_xchg(&assoc->terminating, 1);
> @@ -1207,19 +1201,23 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> if (terminating)
> return;
>
> - spin_lock_irqsave(&tgtport->lock, flags);
> +
> for (i = NVMET_NR_QUEUES; i >= 0; i--) {
> - queue = assoc->queues[i];
> - if (queue) {
> - if (!nvmet_fc_tgt_q_get(queue))
> - continue;
> - spin_unlock_irqrestore(&tgtport->lock, flags);
> - nvmet_fc_delete_target_queue(queue);
> - nvmet_fc_tgt_q_put(queue);
> - spin_lock_irqsave(&tgtport->lock, flags);
> + rcu_read_lock();
> + queue = rcu_dereference(assoc->queues[i]);
> + if (!queue) {
> + rcu_read_unlock();
> + continue;
> + }
> +
> + if (!nvmet_fc_tgt_q_get(queue)) {
> + rcu_read_unlock();
> + continue;
> }
> + rcu_read_unlock();
> + nvmet_fc_delete_target_queue(queue);
> + nvmet_fc_tgt_q_put(queue);
> }
> - spin_unlock_irqrestore(&tgtport->lock, flags);
>
> dev_info(tgtport->dev,
> "{%d:%d} Association deleted\n",
> @@ -1234,10 +1232,9 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> {
> struct nvmet_fc_tgt_assoc *assoc;
> struct nvmet_fc_tgt_assoc *ret = NULL;
> - unsigned long flags;
>
> - spin_lock_irqsave(&tgtport->lock, flags);
> - list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
> + rcu_read_lock();
> + list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
> if (association_id == assoc->association_id) {
> ret = assoc;
> if (!nvmet_fc_tgt_a_get(assoc))
> @@ -1245,7 +1242,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> break;
> }
> }
> - spin_unlock_irqrestore(&tgtport->lock, flags);
> + rcu_read_unlock();
>
> return ret;
> }
> @@ -1473,19 +1470,17 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> static void
> __nvmet_fc_free_assocs(struct nvmet_fc_tgtport *tgtport)
> {
> - struct nvmet_fc_tgt_assoc *assoc, *next;
> - unsigned long flags;
> + struct nvmet_fc_tgt_assoc *assoc;
>
> - spin_lock_irqsave(&tgtport->lock, flags);
> - list_for_each_entry_safe(assoc, next,
> - &tgtport->assoc_list, a_list) {
> + rcu_read_lock();
> + list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
> if (!nvmet_fc_tgt_a_get(assoc))
> continue;
> if (!schedule_work(&assoc->del_work))
> /* already deleting - release local reference */
> nvmet_fc_tgt_a_put(assoc);
> }
> - spin_unlock_irqrestore(&tgtport->lock, flags);
> + rcu_read_unlock();
> }
>
> /**
> @@ -1568,16 +1563,16 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
> continue;
> spin_unlock_irqrestore(&nvmet_fc_tgtlock, flags);
>
> - spin_lock_irqsave(&tgtport->lock, flags);
> - list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
> - queue = assoc->queues[0];
> + rcu_read_lock();
> + list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
> + queue = rcu_dereference(assoc->queues[0]);
> if (queue && queue->nvme_sq.ctrl == ctrl) {
> if (nvmet_fc_tgt_a_get(assoc))
> found_ctrl = true;
> break;
> }
> }
> - spin_unlock_irqrestore(&tgtport->lock, flags);
> + rcu_read_unlock();
>
> nvmet_fc_tgtport_put(tgtport);
>
> --
> 1.9.3
---end quoted text---