edac: core: remove completion-wait for complete with rcu_barrier

Module edac_core.ko uses call_rcu() callbacks in edac_device.c, edac_mc.c
and edac_pci.c.

They all use a wait_for_completion() scheme, but this scheme it not 100%
safe on multiple CPUs. See the _rcu_barrier() implementation which
explains why extra precausion is needed.

The patch adds a comment about rcu_barrier() and as a precausion calls
rcu_barrier(). A maintainer needs to look at removing the
wait_for_completion code.

[[e-mail]: remove the wait_for_completion code]
Signed-off-by Jesper Dangaard Brouer <[e-mail]>
Signed-off-by: Doug Thompson <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/edac/edac_device.c

···
 
 	edac_dev = container_of(head, struct edac_device_ctl_info, rcu);
 	INIT_LIST_HEAD(&edac_dev->link);
-	complete(&edac_dev->removal_complete);
 }
 
 /*
···
 						*edac_device)
 {
 	list_del_rcu(&edac_device->link);
-
-	init_completion(&edac_device->removal_complete);
 	call_rcu(&edac_device->rcu, complete_edac_device_list_del);
-	wait_for_completion(&edac_device->removal_complete);
+	rcu_barrier();
 }
 
 /*

drivers/edac/edac_mc.c

···
 
 	mci = container_of(head, struct mem_ctl_info, rcu);
 	INIT_LIST_HEAD(&mci->link);
-	complete(&mci->complete);
 }
 
 static void del_mc_from_global_list(struct mem_ctl_info *mci)
 {
 	atomic_dec(&edac_handlers);
 	list_del_rcu(&mci->link);
-	init_completion(&mci->complete);
 	call_rcu(&mci->rcu, complete_mc_list_del);
-	wait_for_completion(&mci->complete);
+	rcu_barrier();
 }
 
 /**

drivers/edac/edac_pci.c

···
 
 	pci = container_of(head, struct edac_pci_ctl_info, rcu);
 	INIT_LIST_HEAD(&pci->link);
-	complete(&pci->complete);
 }
 
 /*
···
 static void del_edac_pci_from_global_list(struct edac_pci_ctl_info *pci)
 {
 	list_del_rcu(&pci->link);
-	init_completion(&pci->complete);
 	call_rcu(&pci->rcu, complete_edac_pci_list_del);
-	wait_for_completion(&pci->complete);
+	rcu_barrier();
 }
 
 #if 0