[PATCH v3] xen/gntdev: Ignore failure to unmap INVALID_GRANT_HANDLE

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

The error paths of gntdev_mmap() can call unmap_grant_pages() even
though not all of the pages have been successfully mapped.  This will
trigger the WARN_ON()s in __unmap_grant_pages_done().  The number of
warnings can be very large; I have observed thousands of lines of
warnings in the systemd journal.

Avoid this problem by only warning on unmapping failure if the handle
being unmapped is not INVALID_GRANT_HANDLE.  The handle field of any
page that was not successfully mapped will be INVALID_GRANT_HANDLE, so
this catches all cases where unmapping can legitimately fail.

Suggested-by: Juergen Gross <jgross@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
---
 drivers/xen/gntdev.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Changes since v2:

- Use unmap_ops instead of kunmap_ops in the first WARN_ON

Changes since v1:

- Explicitly check for a status other than GNTST_okay instead of
  implicitly checking that it is nonzero.
- Avoid wrapping a line as within a comparison, as this makes the code
  hard to read.

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 
4b56c39f766d4da68570d08d963f6ef40c8d9c37..84b143eef395b1585f3a8c0fdcb301ce9fbc52ec
 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -396,13 +396,15 @@ static void __unmap_grant_pages_done(int result,
        unsigned int offset = data->unmap_ops - map->unmap_ops;
 
        for (i = 0; i < data->count; i++) {
-               WARN_ON(map->unmap_ops[offset+i].status);
+               WARN_ON(map->unmap_ops[offset + i].status != GNTST_okay &&
+                       map->unmap_ops[offset + i].handle != 
INVALID_GRANT_HANDLE);
                pr_debug("unmap handle=%d st=%d\n",
                        map->unmap_ops[offset+i].handle,
                        map->unmap_ops[offset+i].status);
                map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
                if (use_ptemod) {
-                       WARN_ON(map->kunmap_ops[offset+i].status);
+                       WARN_ON(map->kunmap_ops[offset + i].status != 
GNTST_okay &&
+                               map->kunmap_ops[offset + i].handle != 
INVALID_GRANT_HANDLE);
                        pr_debug("kunmap handle=%u st=%d\n",
                                 map->kunmap_ops[offset+i].handle,
                                 map->kunmap_ops[offset+i].status);
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab