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 <[email protected]>
---
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);
--
1.8.5.6
