Address ZFS race condition

This change adds a patch that reverts a change to the Linux kernel that
was intended to clean-up some internal behavior. Unfortunately, ZFS
currently relies on this behavior to perform correctly.

Without this patch, zvol links might not be created correctly due to a
race condition.

See #183 for more information about this issue.

debian/patches/pve/0006-Revert-block-remove-the-ERESTARTSYS-handling-in-blkd.patch

@@ -0,0 +1,38 @@
+From 92557ee787b409ab4e0cec33d13b483ef80e6d6e Mon Sep 17 00:00:00 2001
+From: Fabian Mastenbroek <[email protected]>
+Date: Mon, 8 Nov 2021 17:16:32 +0100
+Subject: [PATCH] Revert "block: remove the -ERESTARTSYS handling in
+ blkdev_get_by_dev"
+
+This reverts commit a8ed1a0607cfa5478ff6009539f44790c4d0956d.
+---
+ block/bdev.c | 6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/block/bdev.c b/block/bdev.c
+index 485a258b0ab3..f93165f05987 100644
+--- a/block/bdev.c
++++ b/block/bdev.c
+@@ -800,6 +800,10 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
+ 	if (ret)
+ 		return ERR_PTR(ret);
+
++	/*
++	 * If we lost a race with 'disk' being deleted, try again.  See md.c.
++	 */
++retry:
+ 	bdev = blkdev_get_no_open(dev);
+ 	if (!bdev)
+ 		return ERR_PTR(-ENXIO);
+@@ -852,6 +856,8 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
+ 	disk_unblock_events(disk);
+ put_blkdev:
+ 	blkdev_put_no_open(bdev);
++	if (ret == -ERESTARTSYS)
++		goto retry;
+ 	return ERR_PTR(ret);
+ }
+ EXPORT_SYMBOL(blkdev_get_by_dev);
+-- 
+2.33.1
+

debian/patches/series.linux

@@ -3,3 +3,4 @@ pve/0002-bridge-keep-MAC-of-first-assigned-port.patch
 pve/0003-pci-Enable-overrides-for-missing-ACS-capabilities-4..patch
 pve/0004-kvm-disable-default-dynamic-halt-polling-growth.patch
 pve/0005-net-core-downgrade-unregister_netdevice-refcount-lea.patch
+pve/0006-Revert-block-remove-the-ERESTARTSYS-handling-in-blkd.patch