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Linus Torvalds 1c27f1fc15 iov_iter: fix build issue due to possible type mis-match 
Commit 6c77676645 ("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: Linus Torvalds <torvalds@linux-foundation.org>
2022-06-11 10:30:20 -07:00
arch arm64 fixes for 5.19-rc2: 2022-06-10 11:03:51 -07:00
block block: remove bioset_init_from_src 2022-06-08 14:04:14 -04:00
certs certs: Convert spaces in certs/Makefile to a tab 2022-06-10 11:42:02 -07:00
crypto This update includes the following changes: 2022-05-27 18:06:49 -07:00
Documentation netfs: Rename the netfs_io_request cleanup op and give it an op pointer 2022-06-10 20:55:21 +01:00
drivers - Fix DM core's bioset initialization so that blk integrity pool is 2022-06-10 16:32:49 -07:00
fs Notable changes: 2022-06-10 17:28:43 -07:00
include Notable changes: 2022-06-10 17:28:43 -07:00
init gcc-12: disable '-Warray-bounds' universally for now 2022-06-09 10:11:12 -07:00
ipc These changes update the ipc sysctls so that they are fundamentally 2022-06-03 15:54:57 -07:00
kernel Power management fixes for 5.19-rc2 2022-06-10 11:49:27 -07:00
lib iov_iter: fix build issue due to possible type mis-match 2022-06-11 10:30:20 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/huge_memory: Fix xarray node memory leak 2022-06-09 16:24:25 -04:00
net Notable changes: 2022-06-10 17:28:43 -07:00
samples drm for 5.19-rc1 2022-05-25 16:18:27 -07:00
scripts cert host tools: Stop complaining about deprecated OpenSSL functions 2022-06-08 13:18:39 -07:00
security KEYS: trusted: tpm2: Fix migratable logic 2022-06-08 14:12:13 +03:00
sound sound fixes for 5.19-rc2 2022-06-10 10:20:57 -07:00
tools Networking fixes for 5.19-rc2, including fixes from bpf and netfilter. 2022-06-09 12:06:52 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt * Fix syzkaller NULL pointer dereference 2022-06-08 09:16:31 -07:00
.clang-format clang-format: Fix space after for_each macros 2022-05-20 19:27:16 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap Hot fixes for 5.19-rc1. 2022-06-05 17:05:38 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Notable changes: 2022-06-10 17:28:43 -07:00
Makefile gcc-12: disable '-Warray-bounds' universally for now 2022-06-09 10:11:12 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.