Re: mainline build failure due to 6c77676645ad ("iov_iter: Fix iter_xarray_get_pages{,_alloc}()")

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

On Sat, Jun 11, 2022 at 11:45:03AM +0100, Sudip Mukherjee wrote:
> Hi All,
> 
> The latest mainline kernel branch fails to build for "arm allmodconfig",
> "xtensa allmodconfig" and "csky allmodconfig" with the error:
> 
> In file included from ./include/linux/kernel.h:26,
>                  from ./include/linux/crypto.h:16,
>                  from ./include/crypto/hash.h:11,
>                  from lib/iov_iter.c:2:
> 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)))
>       |                                   ^~
> ./include/linux/minmax.h:26:18: note: in expansion of macro '__typecheck'
>    26 |                 (__typecheck(x, y) && __no_side_effects(x, y))
>       |                  ^~~~~~~~~~~
> ./include/linux/minmax.h:36:31: note: in expansion of macro '__safe_cmp'
>    36 |         __builtin_choose_expr(__safe_cmp(x, y), \
>       |                               ^~~~~~~~~~
> ./include/linux/minmax.h:45:25: note: in expansion of macro '__careful_cmp'
>    45 | #define min(x, y)       __careful_cmp(x, y, <)
>       |                         ^~~~~~~~~~~~~
> lib/iov_iter.c:1464:16: note: in expansion of macro 'min'
>  1464 |         return min(nr * PAGE_SIZE - offset, maxsize);
>       |                ^~~
> lib/iov_iter.c: In function 'iter_xarray_get_pages_alloc':
> ./include/linux/minmax.h:20:35: error: comparison of distinct pointer types lacks a cast [-Werror]
>    20 |         (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
>       |                                   ^~
> ./include/linux/minmax.h:26:18: note: in expansion of macro '__typecheck'
>    26 |                 (__typecheck(x, y) && __no_side_effects(x, y))
>       |                  ^~~~~~~~~~~
> ./include/linux/minmax.h:36:31: note: in expansion of macro '__safe_cmp'
>    36 |         __builtin_choose_expr(__safe_cmp(x, y), \
>       |                               ^~~~~~~~~~
> ./include/linux/minmax.h:45:25: note: in expansion of macro '__careful_cmp'
>    45 | #define min(x, y)       __careful_cmp(x, y, <)
>       |                         ^~~~~~~~~~~~~
> lib/iov_iter.c:1628:16: note: in expansion of macro 'min'
>  1628 |         return min(nr * PAGE_SIZE - offset, maxsize);
> 
> 
> git bisect pointed to 6c77676645ad ("iov_iter: Fix iter_xarray_get_pages{,_alloc}()")

At a guess, should be
	return min((size_t)nr * PAGE_SIZE - offset, maxsize);

in both places.  I'm more than half-asleep right now; could you verify that it
(as the last lines of both iter_xarray_get_pages() and iter_xarray_get_pages_alloc())
builds correctly?