iov_iter: fix build issue due to possible type mis-match
Commit 6c776766 ("iov_iter: Fix iter_xarray_get_pages{,_alloc}()") introduced a problem on some 32-bit architectures (at least arm, xtensa, csky,sparc and mips), that have a 'size_t' that is 'unsigned int'. The reason is that we now do min(nr * PAGE_SIZE - offset, maxsize); where 'nr' and 'offset' and both 'unsigned int', and PAGE_SIZE is 'unsigned long'. As a result, the normal C type rules means that the first argument to 'min()' ends up being 'unsigned long'. In contrast, 'maxsize' is of type 'size_t'. Now, 'size_t' and 'unsigned long' are always the same physical type in the kernel, so you'd think this doesn't matter, and from an actual arithmetic standpoint it doesn't. But on 32-bit architectures 'size_t' is commonly 'unsigned int', even if it could also be 'unsigned long'. In that situation, both are unsigned 32-bit types, but they are not the *same* type. And as a result 'min()' will complain about the distinct types (ignore the "pointer types" part of the error message: that's an artifact of the way we have made 'min()' check types for being the same): lib/iov_iter.c: In function 'iter_xarray_get_pages': include/linux/minmax.h:20:35: error: comparison of distinct pointer types lacks a cast [-Werror] 20 | (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) | ^~ lib/iov_iter.c:1464:16: note: in expansion of macro 'min' 1464 | return min(nr * PAGE_SIZE - offset, maxsize); | ^~~ This was not visible on 64-bit architectures (where we always define 'size_t' to be 'unsigned long'). Force these cases to use 'min_t(size_t, x, y)' to make the type explicit and avoid the issue. [ Nit-picky note: technically 'size_t' doesn't have to match 'unsigned long' arithmetically. We've certainly historically seen environments with 16-bit address spaces and 32-bit 'unsigned long'. Similarly, even in 64-bit modern environments, 'size_t' could be its own type distinct from 'unsigned long', even if it were arithmetically identical. So the above type commentary is only really descriptive of the kernel environment, not some kind of universal truth for the kinds of wild and crazy situations that are allowed by the C standard ] Reported-by:Sudip Mukherjee <sudipm.mukherjee@gmail.com> Link: https://lore.kernel.org/all/YqRyL2sIqQNDfky2@debian/ Cc: Jeff Layton <jlayton@kernel.org> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: