Re: linux-next: build failure after merge of the nvdimm tree

[Al Viro <viro@ZenIV.linux.org.uk>]

On Mon, Apr 24, 2017 at 04:11:30PM +1000, Stephen Rothwell wrote:
> Hi Dan,
> 
> After merging the nvdimm tree, today's linux-next build (x86_64
> allmodconfig) failed like this:
> 
> drivers/nvdimm/x86.c: In function 'pmem_from_user':
> drivers/nvdimm/x86.c:115:11: error: implicit declaration of function '__copy_from_user_nocache' [-Werror=implicit-function-declaration]
>   int rc = __copy_from_user_nocache(dst, src, size);
>            ^
> 
> Caused by commit
> 
>   6e704ff67315 ("uio, libnvdimm, pmem: implement cache bypass for all copy_from_iter() operations")
> 
> interacting with commit
> 
>   3f763453e6f2 ("kill __copy_from_user_nocache()")
> 
> from the vfs tree.
> 
> I have no idea why Al removed that function,

Because the entire nocache pile is messy and misguided and the fewer of
those we have, the easier it will be to untangle the damn thing.  This
particular turdlet had no users in mainline.  Unfortunately, it has
grown one in nvdimm, so we'll probably have to drop that removal for now
and hope that it won't be too painful to untangle come next cycle.

Oh, well...  Guess we'll need to resurrect memcpy_nocache() threads from
December and deal witht that mess for good.