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>>>>>>>> + struct ionic_cq *cq, *cq_tmp; >>>>>>>> + LIST_HEAD(flush_list); >>>>>>>> + unsigned long index; >>>>>>>> + >>>>>>>> + /* Flush qp send and recv */ >>>>>>>> + rcu_read_lock(); >>>>>>>> + xa_for_each(&dev->qp_tbl, index, qp) { >>>>>>>> + kref_get(&qp->qp_kref); >>>>>>>> + list_add_tail(&qp->ibkill_flush_ent, &flush_list); >>>>>>>> + } >>>>>>>> + rcu_read_unlock(); >>>>>>> Same question as for CQ. What does RCU lock protect here? >>>>>> It should protect the kref_get against free of qp. The qp memory must >>>>>> be RCU freed. >>>>> I'm not sure that this was intension here. Let's wait for an answer from the author. >>>> As Jason mentioned, It was intended to protect the kref_get against free of >>>> cq and qp >>>> in the destroy path. >>> How is it possible? IB/core is supposed to protect from accessing verbs >>> resources post their release/destroy. >>> >>> After you answered what RCU is protecting, I don't see why you would >>> have custom kref over QP/CQ/e.t.c objects. >>> >>> Thanks >> The RCU protected kref here is making sure that all the hw events are >> processed before destroy callback returns. Similarly, when driver is >> going for ib_unregister_device, it is draining the pending WRs and events. > I asked why do you have kref in first place? When ib_unregister_device > is called all "pending MR" already supposed to be destroyed. > > Thansk The custom kref on QP/CQ object is holding the completion for the destroy callback. If any pending async hw events are being processed, destroy would wait on this completion before it returns. Thanks