xen-blkback: Apply 'feature_persistent' parameter when connect

commit e94c6101e151b019b8babc518ac2a6ada644a5a1 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 aac8a70db24b ("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: aac8a70db24b ("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 a74dfe52dd76d4ecbe89464e6c0b1325cd6bb589..ca7f12aeb2dada1d699fc3f791ad05a81fb561e7 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 <sj@kernel.org>
 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 b3f45d8ea42555125b15bdce901f00cf8c90adf8..7e0d1eb29d8fbb39a5a5276780c2320e044e5887 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;
 }
 
@@ -1090,10 +1088,9 @@ 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;