nvidia-331-uvm 331.20-0ubuntu1: nvidia-331-uvm kernel module failed to build [error: incompatible types when assigning to type ‘uid_t’ from type ‘kuid_t’]

It works in 3.11.10 kernel.

The module that fails to build is the uvm module. The nvidia-331-updates-331 module seems to build quite successfully, and produce the correct module.

Here is a recent make log from an affected machine. Is there any other diagnositic info that would help to resolve this issue?

The uvm module is the one that fails to build.

Support for the latest kernels has been added with 331.20-0ubuntu8 driver into Trusty.

The buildfix_kernel_3.12.patch breaks building on vanilla 3.12 kernels. The module builds fine without it on 3.12.6

In file included from /var/lib/dkms/nvidia-331-updates-uvm/331.20/build/nvidia_uvm_common.h:49:0,
                 from /var/lib/dkms/nvidia-331-updates-uvm/331.20/build/nvidia_uvm_lite.c:26:
/var/lib/dkms/nvidia-331-updates-uvm/331.20/build/nvidia_uvm_lite.c: In function ‘uvmlite_open’:
/var/lib/dkms/nvidia-331-updates-uvm/331.20/build/nvidia_uvm_linux.h:395:70: error: request for member ‘val’ in something not a structure or union
     (((typeof(*current->cred) __force __kernel *)current->cred)->euid.val)
                                                                      ^
/var/lib/dkms/nvidia-331-updates-uvm/331.20/build/nvidia_uvm_lite.c:1326:39: note: in expansion of macro ‘NV_CURRENT_EUID’
     pUvmPrivate->processRecord.euid = NV_CURRENT_EUID();
                                       ^
make[3]: *** [/var/lib/dkms/nvidia-331-updates-uvm/331.20/build/nvidia_uvm_lite.o] Error 1

So it looks like the buildfix_kernel_3.12.patch is missing a check for CONFIG_UIDGID_STRICT_TYPE_CHECKS. The change to kuid_t only happens if that config flag is enabled.

I dug through git, and kuid_t/kgid_t were introduced in kernel 3.5. The proper thing to do is to call __kuid_val(uid) to convert to uid_t on these kernels. The bug isn't a problem introduced with kernel 3.12. It is a problem with all kernels compiled with CONFIG_UIDGID_STRICT_TYPE_CHECKS. This patch should fix the problem for both cases.

Nice catch.

While we're at it, instead of checking the kernel version, we can simply do #ifdef CONFIG_UIDGID_STRICT_TYPE_CHECKS and use __kuid_val (which in turn only does "return uid.val")

This bug was fixed in the package nvidia-graphics-drivers-331-updates - 331.20-0ubuntu9

---------------
nvidia-graphics-drivers-331-updates (331.20-0ubuntu9) trusty; urgency=low

  * debian/dkms_nvidia_uvm/patches/buildfix_kernel_3.12.patch:
    - Apparently the kuid change doesn't affect only Linux >= 3.12.
      Let's check CONFIG_UIDGID_STRICT_TYPE_CHECKS and act
      accordingly (LP: #1252664).
      Thanks to Joseph Yasi for spotting the problem and
      suggesting a fix.
 -- Alberto Milone <email address hidden> Thu, 09 Jan 2014 12:31:09 +0100

So the reason I decided to check for kernel version instead of CONFIG_UIDGID_STRICT_TYPE_CHECKS was for possible future proofing. If the kernel in the future fragments with yet another config option for kuid_t, they would likely implement another __kuid_val function for that, and the patch would still work. Granted, we aren't guaranteed that something else won't break in a kernel API change, so it probably doesn't matter.