xen/blkfront: When purging persistent grants, keep them in the buffer

Boris Ostrovsky · axboe · commit f151ba989d14 · 2018-09-27T08:26:38.000-06:00
Commit a46b536 ("xen/blkfront: cleanup stale persistent grants") added support for purging persistent grants when they are not in use. As part of the purge, the grants were removed from the grant buffer, This eventually causes the buffer to become empty, with BUG_ON triggered in get_free_grant(). This can be observed even on an idle system, within 20-30 minutes. We should keep the grants in the buffer when purging, and only free the grant ref. Fixes: a46b536 ("xen/blkfront: cleanup stale persistent grants") Reviewed-by: Juergen Gross <jgross@suse.com> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
@@ -2667,11 +2667,9 @@ static void purge_persistent_grants(struct blkfront_info *info)
 			    gnttab_query_foreign_access(gnt_list_entry->gref))
 				continue;
 
-			list_del(&gnt_list_entry->node);
 			gnttab_end_foreign_access(gnt_list_entry->gref, 0, 0UL);
+			gnt_list_entry->gref = GRANT_INVALID_REF;
 			rinfo->persistent_gnts_c--;
-			__free_page(gnt_list_entry->page);
-			kfree(gnt_list_entry);
 		}
 
 		spin_unlock_irqrestore(&rinfo->ring_lock, flags);
