> > This RFC series attempts to address the deadlock issue discovered > > while testing nvmf/rdma handling rdma device removal events from > > the rdma_cm. > > Thanks for doing this Steve! > > > For a discussion of the deadlock that can happen, see > > > > http://lists.infradead.org/pipermail/linux-nvme/2016-July/005440.html. > > > > For my description of the deadlock itself, see this post in the above thread: > > > > http://lists.infradead.org/pipermail/linux-nvme/2016-July/005465.html > > > > In a nutshell, iw_cxgb4 and the iw_cm block during qp/cm_id destruction > > until all references are removed. This combined with the iwarp CM passing > > disconnect events up to the rdma_cm during disconnect and/or qp/cm_id > destruction > > leads to a deadlock. > > > > My proposed solution is to remove the need for iw_cxgb4 and iw_cm to > > block during object destruction for the recnts to reach 0, but rather to > > let the freeing of the object memory be deferred when the last deref is > > done. This allows all the qps/cm_ids to be destroyed without blocking, and > > all the object memory freeing ends up happinging when the application's > > device_remove event handler function returns to the rdma_cm. > > This sounds like a very good approach moving forward. > > > Sean, I was hoping you could have a look at the iwcm.c patch particularly, > > to tell my why its broken. :) I spent some time trying to figure out > > why we really need the CALLBACK_DESTROY flag, but I concluded it really > > isn't needed. The one side effect I see with my change, is that the > > application could possibly get a cm_id event after it has destroyed the > > cm_id. There probably is a way to discard events that have a reference > > on the cm_id but get processed after the app has destoyed the cm_id by > > having a new flag indicating "destroyed by app". > By the way, I think Sean is on sabbatical until 9/12. > That sounds easy enough. Does this mean that iwcm relies on the driver > to do this or is it inter-operable with the existing logic? If not this > will need to take care of all the iWARP drivers. This can be handled all in the iw_cm module. In fact, I'm testing a new version of the iw_cm patch now. Steve. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html