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Linus Torvalds e77d587a2c mm: avoid gcc complaint about pointer casting 
The migration code ends up temporarily stashing information of the wrong
type in unused fields of the newly allocated destination folio.  That
all works fine, but gcc does complain about the pointer type mis-use:

    mm/migrate.c: In function ‘__migrate_folio_extract’:
    mm/migrate.c:1050:20: note: randstruct: casting between randomized structure pointer types (ssa): ‘struct anon_vma’ and ‘struct address_space’

     1050 |         *anon_vmap = (void *)dst->mapping;
          |         ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

and gcc is actually right to complain since it really doesn't understand
that this is a very temporary special case where this is ok.

This could be fixed in different ways by just obfuscating the assignment
sufficiently that gcc doesn't see what is going on, but the truly
"proper C" way to do this is by explicitly using a union.

Using unions for type conversions like this is normally hugely ugly and
syntactically nasty, but this really is one of the few cases where we
want to make it clear that we're not doing type conversion, we're really
re-using the value bit-for-bit just using another type.

IOW, this should not become a common pattern, but in this one case using
that odd union is probably the best way to document to the compiler what
is conceptually going on here.

[ Side note: there are valid cases where we convert pointers to other
  pointer types, notably the whole "folio vs page" situation, where the
  types actually have fundamental commonalities.

  The fact that the gcc note is limited to just randomized structures
  means that we don't see equivalent warnings for those cases, but it
  migth also mean that we miss other cases where we do play these kinds
  of dodgy games, and this kind of explicit conversion might be a good
  idea. ]

I verified that at least for an allmodconfig build on x86-64, this
generates the exact same code, apart from line numbers and assembler
comment changes.

Fixes: 64c8902ed4 ("migrate_pages: split unmap_and_move() to _unmap() and _move()")
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2023-03-04 14:03:27 -08:00
..
damon mm/damon/paddr: fix missing folio_put() 2023-02-27 17:00:14 -08:00
kasan kasan: test: fix test for new meminstrinsic instrumentation 2023-03-02 21:54:22 -08:00
kfence hardening updates for v6.2-rc1 2022-12-14 12:20:00 -08:00
kmsan kmsan: disable ftrace in kmsan core code 2023-02-20 12:46:16 -08:00
backing-dev.c mm: add /sys/class/bdi/<bdi>/min_ratio_fine knob 2022-11-30 15:59:06 -08:00
balloon_compaction.c
bootmem_info.c
cma.c mm/cma: fix potential memory loss on cma_declare_contiguous_nid 2023-02-02 22:33:24 -08:00
cma.h
cma_debug.c
cma_sysfs.c
compaction.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
debug.c mm: export dump_mm() 2023-02-09 16:51:40 -08:00
debug_page_ref.c
debug_vm_pgtable.c mm: remove __HAVE_ARCH_PTE_SWP_EXCLUSIVE 2023-02-02 22:33:11 -08:00
dmapool.c
early_ioremap.c
fadvise.c mm: support POSIX_FADV_NOREUSE 2023-01-18 17:12:57 -08:00
failslab.c mm: fix unexpected changes to {failslab|fail_page_alloc}.attr 2022-11-22 18:50:44 -08:00
filemap.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
folio-compat.c mm: change to return bool for isolate_lru_page() 2023-02-20 12:46:17 -08:00
frontswap.c
gup.c mm: change to return bool for folio_isolate_lru() 2023-02-20 12:46:17 -08:00
gup_test.c mm/gup_test: free memory allocated via kvcalloc() using kvfree() 2022-12-15 16:37:48 -08:00
gup_test.h mm/gup_test: start/stop/read functionality for PIN LONGTERM test 2022-11-08 17:37:15 -08:00
highmem.c highmem: fix kmap_to_page() for kmap_local_page() addresses 2022-10-12 18:51:51 -07:00
hmm.c mm/hugetlb: make walk_hugetlb_range() safe to pmd unshare 2023-01-18 17:12:39 -08:00
huge_memory.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
hugetlb.c mm: hugetlb: change to return bool for isolate_hugetlb() 2023-02-20 12:46:17 -08:00
hugetlb_cgroup.c mm/hugetlb: increase use of folios in alloc_huge_page() 2023-02-13 15:54:27 -08:00
hugetlb_vmemmap.c sysctl: fix proc_dobool() usability 2023-02-21 13:34:07 -08:00
hugetlb_vmemmap.h
hwpoison-inject.c mm/hwpoison: add __init/__exit annotations to module init/exit funcs 2022-10-03 14:03:05 -07:00
init-mm.c
internal.h - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
interval_tree.c
io-mapping.c
ioremap.c
Kconfig zsmalloc: set default zspage chain size to 8 2023-02-02 22:33:23 -08:00
Kconfig.debug mm: move KMEMLEAK's Kconfig items from lib to mm 2023-02-02 22:33:26 -08:00
khugepaged.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
kmemleak.c lib/stackdepot, mm: rename stack_depot_want_early_init 2023-02-16 20:43:49 -08:00
ksm.c Merge branch 'mm-hotfixes-stable' into mm-stable 2023-02-10 15:34:48 -08:00
list_lru.c
maccess.c maccess: Fix writing offset in case of fault in strncpy_from_kernel_nofault() 2022-11-11 11:44:46 -08:00
madvise.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
Makefile mm: memcontrol: drop dead CONFIG_MEMCG_SWAP config symbol 2022-10-03 14:03:36 -07:00
mapping_dirty_helpers.c mm/mmu_notifier: remove unused mmu_notifier_range_update_to_read_only export 2023-02-02 22:32:54 -08:00
memblock.c memblock: small optimizations 2023-02-27 09:34:53 -08:00
memcontrol.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
memfd.c mm/memfd: add write seals when apply SEAL_EXEC to executable memfd 2023-01-18 17:12:37 -08:00
memory-failure.c mm/hwpoison: convert TTU_IGNORE_HWPOISON to TTU_HWPOISON 2023-02-27 17:00:14 -08:00
memory-tiers.c memory tier: release the new_memtier in find_create_memory_tier() 2023-02-09 16:51:40 -08:00
memory.c mm/uffd: fix comment in handling pte markers 2023-02-20 12:46:18 -08:00
memory_hotplug.c mm/memory_hotplug: cleanup return value handing in do_migrate_range() 2023-02-20 12:46:18 -08:00
mempolicy.c mm: hugetlb: change to return bool for isolate_hugetlb() 2023-02-20 12:46:17 -08:00
mempool.c mempool: do not use ksize() for poisoning 2022-11-30 15:58:41 -08:00
memremap.c mm/memremap.c: fix outdated comment in devm_memremap_pages 2023-02-09 16:51:46 -08:00
memtest.c
migrate.c mm: avoid gcc complaint about pointer casting 2023-03-04 14:03:27 -08:00
migrate_device.c mm: change to return bool for isolate_lru_page() 2023-02-20 12:46:17 -08:00
mincore.c fs: port inode_owner_or_capable() to mnt_idmap 2023-01-19 09:24:29 +01:00
mlock.c mm: introduce vm_flags_reset_once to replace WRITE_ONCE vm_flags updates 2023-02-09 16:51:41 -08:00
mm_init.c memory: move hotplug memory notifier priority to same file for easy sorting 2022-11-08 17:37:17 -08:00
mm_slot.h mm: introduce common struct mm_slot 2022-10-03 14:02:43 -07:00
mmap.c mm/mremap: fix dup_anon_vma() in vma_merge() case 4 2023-02-27 17:00:14 -08:00
mmap_lock.c
mmu_gather.c mm: mmu_gather: allow more than one batch of delayed rmaps 2022-12-11 18:12:21 -08:00
mmu_notifier.c mm/mmu_notifier: remove unused mmu_notifier_range_update_to_read_only export 2023-02-02 22:32:54 -08:00
mmzone.c
mprotect.c mm/mprotect: Fix successful vma_merge() of next in do_mprotect_pkey() 2023-02-25 20:16:48 -08:00
mremap.c mm: replace vma->vm_flags direct modifications with modifier calls 2023-02-09 16:51:39 -08:00
msync.c mm/msync: use vma_find() instead of vma linked list 2022-09-26 19:46:25 -07:00
nommu.c mm: replace vma->vm_flags direct modifications with modifier calls 2023-02-09 16:51:39 -08:00
oom_kill.c mm/mmu_notifier: remove unused mmu_notifier_range_update_to_read_only export 2023-02-02 22:32:54 -08:00
page-writeback.c fs: convert writepage_t callback to pass a folio 2023-02-02 22:33:34 -08:00
page_alloc.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
page_counter.c
page_ext.c mm/page_ext: init page_ext early if there are no deferred struct pages 2023-02-02 22:33:22 -08:00
page_idle.c mm: page_idle: convert page idle to use a folio 2023-01-18 17:12:52 -08:00
page_io.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
page_isolation.c mm/page_isolation: fix clang deadcode warning 2022-10-28 13:37:22 -07:00
page_owner.c lib/stackdepot, mm: rename stack_depot_want_early_init 2023-02-16 20:43:49 -08:00
page_poison.c
page_reporting.c mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected() 2023-01-18 17:12:50 -08:00
page_reporting.h
page_table_check.c mm/page_ext: do not allocate space for page_ext->flags if not needed 2023-02-02 22:33:11 -08:00
page_vma_mapped.c mm/hugetlb: introduce hugetlb_walk() 2023-01-18 17:12:39 -08:00
pagewalk.c mm/hugetlb: introduce hugetlb_walk() 2023-01-18 17:12:39 -08:00
percpu-internal.h mm: percpu: fix incorrect size in pcpu_obj_full_size() 2023-02-16 20:43:55 -08:00
percpu-km.c
percpu-stats.c
percpu-vm.c
percpu.c mm: memcontrol: rename memcg_kmem_enabled() 2023-02-16 20:43:56 -08:00
pgalloc-track.h
pgtable-generic.c
process_vm_access.c use less confusing names for iov_iter direction initializers 2022-11-25 13:01:55 -05:00
ptdump.c
readahead.c readahead: convert readahead_expand() to use a folio 2023-02-02 22:33:21 -08:00
rmap.c mm/hwpoison: convert TTU_IGNORE_HWPOISON to TTU_HWPOISON 2023-02-27 17:00:14 -08:00
rodata_test.c mm/rodata_test: use PAGE_ALIGNED() helper 2022-10-03 14:03:05 -07:00
secretmem.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
shmem.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
shrinker_debug.c mm: shrinkers: fix deadlock in shrinker debugfs 2023-02-09 15:56:51 -08:00
shuffle.c mm/shuffle: convert module_param_call to module_param_cb 2022-10-03 14:03:07 -07:00
shuffle.h
slab.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
slab.h mm: memcontrol: rename memcg_kmem_enabled() 2023-02-16 20:43:56 -08:00
slab_common.c mm/kasan: simplify and refine kasan_cache code 2023-01-18 17:12:55 -08:00
slob.c Merge branch 'slab/for-6.1/kmalloc_size_roundup' into slab/for-next 2022-09-29 11:30:55 +02:00
slub.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
sparse-vmemmap.c mm/sparse-vmemmap: generalise vmemmap_populate_hugepages() 2022-12-11 18:12:12 -08:00
sparse.c mm/sparse: fix "unused function 'pgdat_to_phys'" warning 2023-02-02 22:33:29 -08:00
swap.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
swap.h mm: remove the __swap_writepage return value 2023-02-02 22:33:33 -08:00
swap_cgroup.c mm: memcontrol: don't allocate cgroup swap arrays when memcg is disabled 2022-10-03 14:03:36 -07:00
swap_slots.c mm/swap: convert put_swap_page() to put_swap_folio() 2022-10-03 14:02:46 -07:00
swap_state.c swap_state: update shadow_nodes for anonymous page 2023-02-02 22:33:24 -08:00
swapfile.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
truncate.c folio-compat: remove lru_cache_add() 2022-12-11 18:12:13 -08:00
usercopy.c mm: use kstrtobool() instead of strtobool() 2022-11-30 15:58:45 -08:00
userfaultfd.c mm/uffd: detect pgtable allocation failures 2023-01-18 17:12:53 -08:00
util.c mm: fix typo in __vm_enough_memory warning 2023-02-13 15:54:33 -08:00
vmalloc.c - Daniel Verkamp has contributed a memfd series ("mm/memfd: add 2023-02-23 17:09:35 -08:00
vmpressure.c
vmscan.c mm: change to return bool for folio_isolate_lru() 2023-02-20 12:46:17 -08:00
vmstat.c mm: vmscan: split khugepaged stats from direct reclaim stats 2022-11-30 15:58:41 -08:00
workingset.c swap_state: update shadow_nodes for anonymous page 2023-02-02 22:33:24 -08:00
z3fold.c mm: remove PageMovable export 2023-01-18 17:12:57 -08:00
zbud.c zpool: clean out dead code 2022-12-11 18:12:10 -08:00
zpool.c zpool: clean out dead code 2022-12-11 18:12:10 -08:00
zsmalloc.c zsmalloc: make zspage chain size configurable 2023-02-02 22:33:23 -08:00
zswap.c zswap: fix writeback lock ordering for zsmalloc 2022-12-11 18:12:09 -08:00