From 6efaf10f163d9a60d1d4b2a049b194a53537ba1b Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Wed, 19 Oct 2016 14:07:19 +0200 Subject: [PATCH] IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker The memory barrier is not enough to protect queuing works into a destroyed cq kthread. Just imagine the following situation: CPU1 CPU2 rvt_cq_enter() worker = cq->rdi->worker; rvt_cq_exit() rdi->worker = NULL; smp_wmb(); kthread_flush_worker(worker); kthread_stop(worker->task); kfree(worker); // nothing queued yet => // nothing flushed and // happily stopped and freed if (likely(worker)) { // true => read before CPU2 acted cq->notify = RVT_CQ_NONE; cq->triggered++; kthread_queue_work(worker, &cq->comptask); BANG: worker has been flushed/stopped/freed in the meantime. This patch solves this by protecting the critical sections by rdi->n_cqs_lock. It seems that this lock is not much contended and looks reasonable for this purpose. One catch is that rvt_cq_enter() might be called from IRQ context. Therefore we must always take the lock with IRQs disabled to avoid a possible deadlock. Signed-off-by: Petr Mladek Signed-off-by: Doug Ledford --- drivers/infiniband/sw/rdmavt/cq.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-) diff --git a/drivers/infiniband/sw/rdmavt/cq.c b/drivers/infiniband/sw/rdmavt/cq.c index 6d9904a4a0ab..223ec4589fc7 100644 --- a/drivers/infiniband/sw/rdmavt/cq.c +++ b/drivers/infiniband/sw/rdmavt/cq.c @@ -119,18 +119,17 @@ 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. */ - smp_read_barrier_depends(); /* see rvt_cq_exit */ - worker = cq->rdi->worker; - if (likely(worker)) { + spin_lock(&cq->rdi->n_cqs_lock); + if (likely(cq->rdi->worker)) { cq->notify = RVT_CQ_NONE; cq->triggered++; - kthread_queue_work(worker, &cq->comptask); + kthread_queue_work(cq->rdi->worker, &cq->comptask); } + spin_unlock(&cq->rdi->n_cqs_lock); } spin_unlock_irqrestore(&cq->lock, flags); @@ -240,15 +239,15 @@ struct ib_cq *rvt_create_cq(struct ib_device *ibdev, } } - spin_lock(&rdi->n_cqs_lock); + spin_lock_irq(&rdi->n_cqs_lock); if (rdi->n_cqs_allocated == rdi->dparms.props.max_cq) { - spin_unlock(&rdi->n_cqs_lock); + spin_unlock_irq(&rdi->n_cqs_lock); ret = ERR_PTR(-ENOMEM); goto bail_ip; } rdi->n_cqs_allocated++; - spin_unlock(&rdi->n_cqs_lock); + spin_unlock_irq(&rdi->n_cqs_lock); if (cq->ip) { spin_lock_irq(&rdi->pending_lock); @@ -296,9 +295,9 @@ int rvt_destroy_cq(struct ib_cq *ibcq) struct rvt_dev_info *rdi = cq->rdi; kthread_flush_work(&cq->comptask); - spin_lock(&rdi->n_cqs_lock); + spin_lock_irq(&rdi->n_cqs_lock); rdi->n_cqs_allocated--; - spin_unlock(&rdi->n_cqs_lock); + spin_unlock_irq(&rdi->n_cqs_lock); if (cq->ip) kref_put(&cq->ip->ref, rvt_release_mmap_info); else @@ -541,12 +540,15 @@ void rvt_cq_exit(struct rvt_dev_info *rdi) { struct kthread_worker *worker; - worker = rdi->worker; - if (!worker) + /* block future queuing from send_complete() */ + spin_lock_irq(&rdi->n_cqs_lock); + if (!rdi->worker) { + spin_unlock_irq(&rdi->n_cqs_lock); return; - /* blocks future queuing from send_complete() */ + } rdi->worker = NULL; - smp_wmb(); /* See rdi_cq_enter */ + spin_unlock_irq(&rdi->n_cqs_lock); + kthread_flush_worker(worker); kthread_stop(worker->task); kfree(worker); -- 2.30.2