Xen blkfront advertises its support of the persistent grants feature when it first setting up and when resuming in 'talk_to_blkback()'. Then, blkback reads the advertised value when it connects with blkfront and decides if it will use the persistent grants feature or not, and advertises its decision to blkfront. Blkfront reads the blkback's decision and it also makes the decision for the use of the feature.

Commit 402c43ea6b34 ("xen-blkfront: Apply 'feature_persistent' parameter when connect"), however, made the blkfront's read of the parameter for disabling the advertisement, namely 'feature_persistent', to be done when it negotiate, not when advertise. Therefore blkfront advertises without reading the parameter. As the field for caching the parameter value is zero-initialized, it always advertises as the feature is disabled, so that the persistent grants feature becomes always disabled.

This commit fixes the issue by making the blkfront does parmeter caching just before the advertisement.

Fixes: 402c43ea6b34 ("xen-blkfront: Apply 'feature_persistent' parameter when connect") Cc: stable@vger.kernel.org # 5.10.x Reported-by: Marek Marczykowski-Górecki marmarek@invisiblethingslab.com Signed-off-by: SeongJae Park sj@kernel.org --- drivers/block/xen-blkfront.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index dfae08115450..35b9bcad9db9 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -1759,6 +1759,12 @@ static int write_per_ring_nodes(struct xenbus_transaction xbt, return err; }

+/* Enable the persistent grants feature. */ +static bool feature_persistent = true; +module_param(feature_persistent, bool, 0644); +MODULE_PARM_DESC(feature_persistent, + "Enables the persistent grants feature"); + /* Common code used when first setting up, and when resuming. */ static int talk_to_blkback(struct xenbus_device *dev, struct blkfront_info *info) @@ -1850,6 +1856,7 @@ static int talk_to_blkback(struct xenbus_device *dev, message = "writing protocol"; goto abort_transaction; } + info->feature_persistent_parm = feature_persistent; err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", info->feature_persistent_parm); if (err) @@ -1919,12 +1926,6 @@ static int negotiate_mq(struct blkfront_info *info) return 0; }

-/* Enable the persistent grants feature. */ -static bool feature_persistent = true; -module_param(feature_persistent, bool, 0644); -MODULE_PARM_DESC(feature_persistent, - "Enables the persistent grants feature"); - /* * Entry point to this code when a new device is created. Allocate the basic * structures and the ring buffer for communication with the backend, and @@ -2284,7 +2285,6 @@ static void blkfront_gather_backend_features(struct blkfront_info *info) if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0)) blkfront_setup_discard(info);

- info->feature_persistent_parm = feature_persistent; if (info->feature_persistent_parm) info->feature_persistent = !!xenbus_read_unsigned(info->xbdev->otherend,