[Bug 1976248] [NEW] Revert PPC get_user workaround

Public bug reported:

[Impact]

 * A change of kernel symbol license allows to drop a PPC specific
workaround in zfs-dkms to use the regular (better) code paths.

 * See details in:

https://git.launchpad.net/ubuntu/+source/zfs-
linux/tree/debian/patches/4900-ppc-get-user-workaround.patch

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1009242

[Test Plan]

 * linux: apply
https://github.com/torvalds/linux/commit/d9e5c3e9e75162f845880535957b7fd0b4637d23

 * zfs-dkms: revert https://git.launchpad.net/ubuntu/+source/zfs-
linux/tree/debian/patches/4900-ppc-get-user-workaround.patch

 * Build on kernel with zfs module on ppc

 * Ensure that zfs.ko successfully loads and works

 * Test that root on zfs installations work on ppc (however, Ubuntu
currently doesn't provide an installation method to achieve this, so
this bit of verification might be hard to complete)

[Where problems could occur]

* linux: the patch only changes the symbol licensing and the potential
tainteness status of the kernel, without any observable user or kernel
space impacts

 * zfs-dkms: The PPC workaround patch is known to be buggy, and the new
arch-independent codepath may now use optimized codepaths inside kernel
resulting in a different behavior as observed by user-space (operation
successful, EFAULT not returned) matching the behavior of all other
architectures.

** Affects: linux (Ubuntu)
Importance: Undecided
Status: New

** Affects: zfs-linux (Ubuntu)
Importance: Undecided
Status: New

** Also affects: linux (Ubuntu)
Importance: Undecided
Status: New

** Description changed:

[Impact]

- * A change of kernel symbol license allows to drop a PPC specific
+  * A change of kernel symbol license allows to drop a PPC specific
workaround in zfs-dkms to use the regular (better) code paths.

- * See details in:
+  * See details in:

https://git.launchpad.net/ubuntu/+source/zfs-
linux/tree/debian/patches/4900-ppc-get-user-workaround.patch

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1009242

-
[Test Plan]

- * linux: apply https://github.com/torvalds/linux/commit/d9e5c3e9e75162f845880535957b7fd0b4637d23
-
- * zfs-dkms: revert https://git.launchpad.net/ubuntu/+source/zfs-linux/tree/debian/patches/4900-ppc-get-user-workaround.patch
+  * linux: apply
+ https://github.com/torvalds/linux/commit/d9e5c3e9e75162f845880535957b7fd0b4637d23

- * Build on kernel with zfs module on ppc
+  * zfs-dkms: revert https://git.launchpad.net/ubuntu/+source/zfs-
+ linux/tree/debian/patches/4900-ppc-get-user-workaround.patch

- * Ensure that zfs.ko successfully loads and works
+  * Build on kernel with zfs module on ppc

- * Test that root on zfs installations work on ppc (however, Ubuntu
+  * Ensure that zfs.ko successfully loads and works
+
+  * Test that root on zfs installations work on ppc (however, Ubuntu
currently doesn't provide an installation method to achieve this, so
this bit of verification might be hard to complete)

[Where problems could occur]

- * The PPC workaround patch is known to be buggy, and the new arch-
- independent codepath may now use optimized codepaths inside kernel
+ * linux: the patch only changes the symbol licensing and the potential
+ tainteness status of the kernel, without any observable user or kernel
+ space impacts
+
+  * zfs-dkms: The PPC workaround patch is known to be buggy, and the new
+ arch-independent codepath may now use optimized codepaths inside kernel
resulting in a different behavior as observed by user-space (operation
successful, EFAULT not returned) matching the behavior of all other
architectures.

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https://bugs.launchpad.net/bugs/1976248

Title:
Revert PPC get_user workaround

Status in linux package in Ubuntu:
New
Status in zfs-linux package in Ubuntu:
New

Bug description:
[Impact]

 * A change of kernel symbol license allows to drop a PPC specific
workaround in zfs-dkms to use the regular (better) code paths.

 * See details in:

https://git.launchpad.net/ubuntu/+source/zfs-
linux/tree/debian/patches/4900-ppc-get-user-workaround.patch

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1009242

[Test Plan]

 * linux: apply
https://github.com/torvalds/linux/commit/d9e5c3e9e75162f845880535957b7fd0b4637d23

 * zfs-dkms: revert https://git.launchpad.net/ubuntu/+source/zfs-
linux/tree/debian/patches/4900-ppc-get-user-workaround.patch

 * Build on kernel with zfs module on ppc

 * Ensure that zfs.ko successfully loads and works

 * Test that root on zfs installations work on ppc (however, Ubuntu
currently doesn't provide an installation method to achieve this, so
this bit of verification might be hard to complete)

[Where problems could occur]

* linux: the patch only changes the symbol licensing and the
potential tainteness status of the kernel, without any observable user
or kernel space impacts

 * zfs-dkms: The PPC workaround patch is known to be buggy, and the
new arch-independent codepath may now use optimized codepaths inside
kernel resulting in a different behavior as observed by user-space
(operation successful, EFAULT not returned) matching the behavior of
all other architectures.

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