FAILED: patch "[PATCH] xen-blkfront: Cache feature_persistent value before" failed to apply to 5.10-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From fe8f65b018effbf473f53af3538d0c1878b8b329 Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Wed, 31 Aug 2022 16:58:24 +0000
Subject: [PATCH] xen-blkfront: Cache feature_persistent value before
 advertisement
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220831165824.94815-4-sj@kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 276b2ee2a155..1f85750f981e 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,