xen-blkback: Apply 'feature_persistent' parameter when connect

commit d626e33fd447dc9615107d6c3a6316d6ac1f700c upstream.

In some use cases[1], the backend is created while the frontend doesn't
support the persistent grants feature, but later the frontend can be
changed to support the feature and reconnect.  In the past, 'blkback'
enabled the persistent grants feature since it unconditionally checked
if frontend supports the persistent grants feature for every connect
('connect_ring()') and decided whether it should use persistent grans or
not.

However, commit 3d14b04b1cc9 ("xen-blkback: add a parameter for
disabling of persistent grants") has mistakenly changed the behavior.
It made the frontend feature support check to not be repeated once it
shown the 'feature_persistent' as 'false', or the frontend doesn't
support persistent grants.

This commit changes the behavior of the parameter to make effect for
every connect, so that the previous workflow can work again as expected.

[1] https://lore.kernel.org/xen-devel/CAJwUmVB6H3iTs-C+U=v-pwJB7-_ZRHPxHzKRJZ22xEPW7z8a=g@mail.gmail.com/

Reported-by: Andrii Chepurnyi <andrii.chepurnyi82@gmail.com>
Fixes: 3d14b04b1cc9 ("xen-blkback: add a parameter for disabling of persistent grants")
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: Maximilian Heyne <mheyne@amazon.de>
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Maximilian Heyne <mheyne@amazon.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220715225108.193398-3-sj@kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
index ac2947b98950476b5d9988b73df34eb8403165d6..3d5de44cbbee9425615c13da94748131a30e1c70 100644 (file)
--- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
@@ -42,5 +42,5 @@ KernelVersion:  5.10
 Contact:        SeongJae Park <sjpark@amazon.de>
 Description:
                 Whether to enable the persistent grants feature or not.  Note
-                that this option only takes effect on newly created backends.
+                that this option only takes effect on newly connected backends.
                 The default is Y (enable).

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 82696d47046aff8d8fb190e98eb06d9f19b2b011..78b50ac11e1911d6511cb08b8697c0bdec50d674 100644 (file)
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -185,8 +185,6 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
        __module_get(THIS_MODULE);
        INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
 
-       blkif->vbd.feature_gnt_persistent = feature_persistent;
-
        return blkif;
 }
 
@@ -1089,10 +1087,9 @@ static int connect_ring(struct backend_info *be)
                xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
                return -ENOSYS;
        }
-       if (blkif->vbd.feature_gnt_persistent)
-               blkif->vbd.feature_gnt_persistent =
-                       xenbus_read_unsigned(dev->otherend,
-                                       "feature-persistent", 0);
+
+       blkif->vbd.feature_gnt_persistent = feature_persistent &&
+               xenbus_read_unsigned(dev->otherend, "feature-persistent", 0);
 
        blkif->vbd.overflow_max_grants = 0;