Zfs: Linux 5.0: _kernel_fpu{begin,end} no longer exported

[tonyhutter]

System information

Type | Version/Name
--- | ---
Distribution Name | Fedora
Distribution Version | 30 (rawhide)
Linux Kernel | 5.0.0-0.rc1.git0.1.fc30.x86_64
Architecture | x86-64
ZFS Version | master
SPL Version | master

Describe the problem you're observing

The 4.2 kernel refractored the FPU code: https://lwn.net/Articles/643235/ It seems the latest kernels removed the old compatibility headers.

We need to rename our #includes <asm/i387.h> -> <asm/fpu/api.h> and <asm/xcr.h> -> <asm/fpu/internal.h> on newer kernels.

Describe how to reproduce the problem

make on rawhide with ZFS master

Include any warning/errors/backtraces from the system logs

/home/hutter/current_kernel_time64/include/linux/simd_x86.h:98:10: fatal error: asm/i387.h: No such file or directory
 #include <asm/i387.h>
          ^~~~~~~~~~~~
compilation terminated.

[mdionne]

The underlying issue comes from kernel commit 12209993e98c5fa1855c467f22a24e3d5b8be205 ("x86/fpu: Don't export __kernel_fpu_{begin,end}()"), which unexports __kernel_fpu_begin(), and causes the configure tests not to define HAVE_FPU_API_H. Changing the header locations will just lead to another failure later because kernel_fpu_begin/end() are exported GPL, and can't be used directly from the zfs module.

See the thread on LKML starting here: https://marc.info/?l=linux-kernel&m=154689892914091

Marc

[tonyhutter]

@mdionne thanks for bringing this to our attention. Hopefully they change their minds and EXPORT_SYMBOL(kernel_fpu_begin) so we can use that instead.

[ideologysec]

https://marc.info/?l=linux-kernel&m=154714516832389&w=2

Gotta love the replies. Greg K-H:

My tolerance for ZFS is pretty non-existant. Sun explicitly did not
want their code to work on Linux, so why would we do extra work to get
their code to work properly?

[sbuller]

It would be nice if Oracle would just fix the license once and for all.

[tonyhutter]

I think we need to operate under the assumption that they're not going to export the functions, and just disable the vectorized versions of the checksums if _kernel_fpu{begin,end} are not detected.

[tonyhutter]

Looks like the kernel people may have backported their patch to older kernels:

For the record, it appears the FPU export was removed in 4.19.38 (released 2019-05-02) via d4ff57d0320bf441ad5a3084b3adbba4da1d79f8 and 4.14.120 (released 2019-05-16) via a725c5201f0807a9f843db525f5f98f6c7a4c25b.

https://github.com/zfsonlinux/zfs/issues/8793#issuecomment-496709454