xen-blkback: Apply 'feature_persistent' parameter when connect

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 e06da285af58 ("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: e06da285af58 ("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>

diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
index 7faf719af16502c8fe01be06ebf13eabb2487c53..fac0f429a869fd8ce5bc102a65a8a48052ed818b 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:        Maximilian Heyne <mheyne@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 16c6785d260c3cd2c11d508fbc75b7232f02a06c..ee7ad2fb432d1b9b4ab81afc56614fe3d54a0c1c 100644 (file)
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -186,8 +186,6 @@ 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;
 }
 
@@ -1086,10 +1084,9 @@ 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;