xen/blkback: safely unmap purge persistent grants

Commit c43cf3ea8385 ("xen-blkback: safely unmap grants in case they
are still in use") use gnttab_unmap_refs_async() to wait until the
mapped pages are no longer in use before unmapping them, but that
commit missed the persistent case.  Purge persistent pages can't be
unmapped either unless no longer in use.

Signed-off-by: Bob Liu <bob.liu@oracle.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 18 insertions, 6 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index bd2b3bbbb22c..48e98f2712b5 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -329,8 +329,18 @@ void xen_blkbk_unmap_purged_grants(struct work_struct *work)
         struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
         struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
         struct persistent_gnt *persistent_gnt;
-        int ret, segs_to_unmap = 0;
+        int segs_to_unmap = 0;
         struct xen_blkif *blkif = container_of(work, typeof(*blkif), persistent_purge_work);
+        struct gntab_unmap_queue_data unmap_data;
+        struct completion unmap_completion;
+
+        init_completion(&unmap_completion);
+
+        unmap_data.data = &unmap_completion;
+        unmap_data.done = &free_persistent_gnts_unmap_callback;
+        unmap_data.pages = pages;
+        unmap_data.unmap_ops = unmap;
+        unmap_data.kunmap_ops = NULL;
 
         while(!list_empty(&blkif->persistent_purge_list)) {
                 persistent_gnt = list_first_entry(&blkif->persistent_purge_list,
@@ -346,17 +356,19 @@ void xen_blkbk_unmap_purged_grants(struct work_struct *work)
                 pages[segs_to_unmap] = persistent_gnt->page;
 
                 if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
-                        ret = gnttab_unmap_refs(unmap, NULL, pages,
-                                segs_to_unmap);
-                        BUG_ON(ret);
+                        unmap_data.count = segs_to_unmap;
+                        gnttab_unmap_refs_async(&unmap_data);
+                        wait_for_completion(&unmap_completion);
+
                         put_free_pages(blkif, pages, segs_to_unmap);
                         segs_to_unmap = 0;
                 }
                 kfree(persistent_gnt);
         }
         if (segs_to_unmap > 0) {
-                ret = gnttab_unmap_refs(unmap, NULL, pages, segs_to_unmap);
-                BUG_ON(ret);
+                unmap_data.count = segs_to_unmap;
+                gnttab_unmap_refs_async(&unmap_data);
+                wait_for_completion(&unmap_completion);
                 put_free_pages(blkif, pages, segs_to_unmap);
         }
 }