[PATCH] xen/blkback: safely unmap purge persistent grants

[PATCH] xen/blkback: safely unmap purge persistent grants

[Bob Liu]

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>
---
 drivers/block/xen-blkback/blkback.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 2a04d34..f59d7c3 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -327,8 +327,18 @@ 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,
@@ -344,17 +354,19 @@ 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);
 	}
 }
-- 
1.8.3.1

Re: [PATCH] xen/blkback: safely unmap purge persistent grants

[Roger Pau Monné]

Hello,

El 25/03/15 a les 11.02, Bob Liu ha escrit:
> +		gnttab_unmap_refs_async(&unmap_data);
> +		wait_for_completion(&unmap_completion);

I think David had a comment about putting this into some kind of common
helper since it's used widely (at least in blkback). Could you look into it?

Roger.

Re: [PATCH] xen/blkback: safely unmap purge persistent grants

[Bob Liu]

On 03/26/2015 07:15 PM, Roger Pau Monné wrote:
> Hello,
> 
> El 25/03/15 a les 11.02, Bob Liu ha escrit:
>> +		gnttab_unmap_refs_async(&unmap_data);
>> +		wait_for_completion(&unmap_completion);
> 
> I think David had a comment about putting this into some kind of common
> helper since it's used widely (at least in blkback). Could you look into it?
> 

Sure, sorry for forgot that.
I'll send out an new patch soon.

-- 
Regards,
-Bob