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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 <pmladek@suse.com> Signed-off-by: Doug Ledford <dledford@redhat.com> |
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