On Mon, 2015-05-25 at 15:14 -0700, Nicholas A. Bellinger wrote: > On Fri, 2015-05-22 at 13:31 +0200, Christoph Hellwig wrote: > > On Fri, May 22, 2015 at 01:55:30AM -0700, Nicholas A. Bellinger wrote: <SNIP> > > > > > + kref_put(&orig->pr_kref, target_pr_kref_release); > > > > > + wait_for_completion(&orig->pr_comp); > > > > > > > > > > > > > > + kref_put(&orig->pr_kref, target_pr_kref_release); > > > > > /* > > > > > - * Disable struct se_dev_entry LUN ACL mapping > > > > > + * Before fireing off RCU callback, wait for any in process SPEC_I_PT=1 > > > > > + * or REGISTER_AND_MOVE PR operation to complete. > > > > > */ > > > > > + wait_for_completion(&orig->pr_comp); > > > > > + kfree_rcu(orig, rcu_head); > > > > > > > > The release callback should just call kfree_rcu, no need to wait for the > > > > release in the caller. > > > > > > > > > > Why doesn't se_dev_entry release this need to wait for the special case > > > references to drop..? > > > > Why would it? > > It originally had to wait in order for the se_dev_entry consumers to > drop, before it could be reused in se_node_acl->device_list[].. > > > There is no access to the structure at this point, so there > > is no point to keep it around localy. If there were other references to > > it they by defintion don't need it anymore by the time they drop the > > reference count. Freeing a structure as soon as the refcount drops > > zero is the normal style all over the place. Waiting for a reference > > count only makes sense if it's a drain style operation where you don't > > free the structure but you just want to wait for some class of consumers > > to stop using it. > > .. but since it's not being reused anymore, doing a kfree_rcu() from the > final kref_put() should be fine. > > Converting now. Looking at this more while adding rcu notation, just calling kfree_rcu() from kref_put() is not going to work here. The wait_for_completion(&orig->pr_comp) above is still required because core_scsi3_lunacl_depend_item() has to dereference se_deve->se_lun_acl outside of the lock (with se_deve->pr_kref held) to obtain the configfs dependency for se_lun_acl->se_lun_group. Otherwise, se_lun_acl->se_lun_group can be removed from out below the core_scsi3_lunacl_depend_item() caller, if se_deve->pr_comp doesn't wait for the configfs dependency to be released. --nab -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
