rds: ib: Fix NULL pointer dereference in debug code
rds_ib_recv_refill() is a function that refills an IB receive queue. It can be called from both the CQE handler (tasklet) and a worker thread. Just after the call to ib_post_recv(), a debug message is printed with rdsdebug(): ret = ib_post_recv(ic->i_cm_id->qp, &recv->r_wr, &failed_wr); rdsdebug("recv %p ibinc %p page %p addr %lu ret %d\n", recv, recv->r_ibinc, sg_page(&recv->r_frag->f_sg), (long) ib_sg_dma_address( ic->i_cm_id->device, &recv->r_frag->f_sg), ret); Now consider an invocation of rds_ib_recv_refill() from the worker thread, which is preemptible. Further, assume that the worker thread is preempted between the ib_post_recv() and rdsdebug() statements. Then, if the preemption is due to a receive CQE event, the rds_ib_recv_cqe_handler() will be invoked. This function processes receive completions, inc...
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