From: Sebastian Sanchez sebastian.sanchez@intel.com
All threads queuing CQ entries on different CQs are unnecessarily synchronized by a spin lock to check if the CQ kthread worker hasn't been destroyed before queuing an CQ entry.
The lock used in 6efaf10f163d ("IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker") is a device global lock and will have poor performance at scale as completions are entered from a large number of CPUs.
Convert to use RCU where the read side of RCU is rvt_cq_enter() to determine that the worker is alive prior to triggering the completion event. Apply write side RCU semantics in rvt_driver_cq_init() and rvt_cq_exit().
Fixes: 6efaf10f163d ("IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker") Cc: stable@vger.kernel.org # 4.14.x Reviewed-by: Mike Marciniszyn mike.marciniszyn@intel.com Signed-off-by: Sebastian Sanchez sebastian.sanchez@intel.com Signed-off-by: Dennis Dalessandro dennis.dalessandro@intel.com --- drivers/infiniband/sw/rdmavt/cq.c | 31 +++++++++++++++++++------------ include/rdma/rdma_vt.h | 2 +- 2 files changed, 20 insertions(+), 13 deletions(-)
diff --git a/drivers/infiniband/sw/rdmavt/cq.c b/drivers/infiniband/sw/rdmavt/cq.c index fb52b66..340c17a 100644 --- a/drivers/infiniband/sw/rdmavt/cq.c +++ b/drivers/infiniband/sw/rdmavt/cq.c @@ -120,17 +120,20 @@ void rvt_cq_enter(struct rvt_cq *cq, struct ib_wc *entry, bool solicited) if (cq->notify == IB_CQ_NEXT_COMP || (cq->notify == IB_CQ_SOLICITED && (solicited || entry->status != IB_WC_SUCCESS))) { + struct kthread_worker *worker; + /* * This will cause send_complete() to be called in * another thread. */ - spin_lock(&cq->rdi->n_cqs_lock); - if (likely(cq->rdi->worker)) { + rcu_read_lock(); + worker = rcu_dereference(cq->rdi->worker); + if (likely(worker)) { cq->notify = RVT_CQ_NONE; cq->triggered++; - kthread_queue_work(cq->rdi->worker, &cq->comptask); + kthread_queue_work(worker, &cq->comptask); } - spin_unlock(&cq->rdi->n_cqs_lock); + rcu_read_unlock(); }
spin_unlock_irqrestore(&cq->lock, flags); @@ -512,7 +515,7 @@ int rvt_driver_cq_init(struct rvt_dev_info *rdi) int cpu; struct kthread_worker *worker;
- if (rdi->worker) + if (rcu_access_pointer(rdi->worker)) return 0;
spin_lock_init(&rdi->n_cqs_lock); @@ -524,7 +527,7 @@ int rvt_driver_cq_init(struct rvt_dev_info *rdi) return PTR_ERR(worker);
set_user_nice(worker->task, MIN_NICE); - rdi->worker = worker; + RCU_INIT_POINTER(rdi->worker, worker); return 0; }
@@ -536,15 +539,19 @@ void rvt_cq_exit(struct rvt_dev_info *rdi) { struct kthread_worker *worker;
- /* block future queuing from send_complete() */ - spin_lock_irq(&rdi->n_cqs_lock); - worker = rdi->worker; + if (!rcu_access_pointer(rdi->worker)) + return; + + spin_lock(&rdi->n_cqs_lock); + worker = rcu_dereference_protected(rdi->worker, + lockdep_is_held(&rdi->n_cqs_lock)); if (!worker) { - spin_unlock_irq(&rdi->n_cqs_lock); + spin_unlock(&rdi->n_cqs_lock); return; } - rdi->worker = NULL; - spin_unlock_irq(&rdi->n_cqs_lock); + RCU_INIT_POINTER(rdi->worker, NULL); + spin_unlock(&rdi->n_cqs_lock); + synchronize_rcu();
kthread_destroy_worker(worker); } diff --git a/include/rdma/rdma_vt.h b/include/rdma/rdma_vt.h index 3f4c187..eec495e 100644 --- a/include/rdma/rdma_vt.h +++ b/include/rdma/rdma_vt.h @@ -402,7 +402,7 @@ struct rvt_dev_info { spinlock_t pending_lock; /* protect pending mmap list */
/* CQ */ - struct kthread_worker *worker; /* per device cq worker */ + struct kthread_worker __rcu *worker; /* per device cq worker */ u32 n_cqs_allocated; /* number of CQs allocated for device */ spinlock_t n_cqs_lock; /* protect count of in use cqs */