Commit 6efaf10f authored by Petr Mladek's avatar Petr Mladek Committed by Doug Ledford

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: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
parent 66431b0e
......@@ -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);
......
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