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Linus Torvalds cd1adf1b63 Revert "mm/gup: remove try_get_page(), call try_get_compound_head() directly" 
This reverts commit 9857a17f20.

That commit was completely broken, and I should have caught on to it
earlier.  But happily, the kernel test robot noticed the breakage fairly
quickly.

The breakage is because "try_get_page()" is about avoiding the page
reference count overflow case, but is otherwise the exact same as a
plain "get_page()".

In contrast, "try_get_compound_head()" is an entirely different beast,
and uses __page_cache_add_speculative() because it's not just about the
page reference count, but also about possibly racing with the underlying
page going away.

So all the commentary about how

 "try_get_page() has fallen a little behind in terms of maintenance,
  try_get_compound_head() handles speculative page references more
  thoroughly"

was just completely wrong: yes, try_get_compound_head() handles
speculative page references, but the point is that try_get_page() does
not, and must not.

So there's no lack of maintainance - there are fundamentally different
semantics.

A speculative page reference would be entirely wrong in "get_page()",
and it's entirely wrong in "try_get_page()".  It's not about
speculation, it's purely about "uhhuh, you can't get this page because
you've tried to increment the reference count too much already".

The reason the kernel test robot noticed this bug was that it hit the
VM_BUG_ON() in __page_cache_add_speculative(), which is all about
verifying that the context of any speculative page access is correct.
But since that isn't what try_get_page() is all about, the VM_BUG_ON()
tests things that are not correct to test for try_get_page().

Reported-by: kernel test robot <oliver.sang@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2021-09-07 11:03:45 -07:00
..
kasan Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
kfence Kbuild updates for v5.15 2021-09-03 15:33:47 -07:00
Kconfig mm: introduce memfd_secret system call to create "secret" memory areas 2021-07-08 11:48:21 -07:00
Kconfig.debug mm, page_poison: remove CONFIG_PAGE_POISONING_ZERO 2020-12-15 12:13:46 -08:00
Makefile mm: introduce memfd_secret system call to create "secret" memory areas 2021-07-08 11:48:21 -07:00
backing-dev.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
balloon_compaction.c mm: fix typos in comments 2021-05-07 00:26:35 -07:00
bootmem_info.c mm/bootmem_info.c: mark __init on register_page_bootmem_info_section 2021-09-03 09:58:14 -07:00
cleancache.c
…
cma.c mm: use proper type for cma_[alloc|release] 2021-05-05 11:27:24 -07:00
cma.h mm: cma: support sysfs 2021-05-05 11:27:24 -07:00
cma_debug.c mm/cma: change cma mutex to irq safe spinlock 2021-05-05 11:27:21 -07:00
cma_sysfs.c mm: cma: support sysfs 2021-05-05 11:27:24 -07:00
compaction.c mm: compaction: support triggering of proactive compaction by user 2021-09-03 09:58:17 -07:00
debug.c mm/debug: factor PagePoisoned out of __dump_page 2021-06-29 10:53:53 -07:00
debug_page_ref.c
…
debug_vm_pgtable.c mm/debug_vm_pgtable: fix corrupted page flag 2021-09-03 09:58:10 -07:00
dmapool.c mm/dmapool: use DEVICE_ATTR_RO macro 2021-06-29 10:53:52 -07:00
early_ioremap.c mm/early_ioremap.c: use __func__ instead of function name 2021-02-26 09:41:02 -08:00
fadvise.c mm, fadvise: improve the expensive remote LRU cache draining after FADV_DONTNEED 2020-10-13 18:38:29 -07:00
failslab.c
…
filemap.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
frontswap.c mm/mempool: minor coding style tweaks 2021-05-05 11:27:27 -07:00
gup.c Revert "mm/gup: remove try_get_page(), call try_get_compound_head() directly" 2021-09-07 11:03:45 -07:00
gup_test.c selftests/vm: gup_test: test faulting in kernel, and verify pinnable pages 2021-05-05 11:27:26 -07:00
gup_test.h selftests/vm: gup_test: fix test flag 2021-05-05 11:27:26 -07:00
highmem.c mm: fix typos in comments 2021-05-07 00:26:35 -07:00
hmm.c mm: device exclusive memory access 2021-07-01 11:06:03 -07:00
huge_memory.c mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing code 2021-09-03 09:58:13 -07:00
hugetlb.c mm/hugetlb: add support for mempolicy MPOL_PREFERRED_MANY 2021-09-03 09:58:17 -07:00
hugetlb_cgroup.c hugetlb: make free_huge_page irq safe 2021-05-05 11:27:22 -07:00
hugetlb_vmemmap.c mm: hugetlb: introduce CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON 2021-06-30 20:47:26 -07:00
hugetlb_vmemmap.h mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate 2021-06-30 20:47:25 -07:00
hwpoison-inject.c mm: hwpoison: don't drop slab caches for offlining non-LRU page 2021-09-03 09:58:15 -07:00
init-mm.c mm: add setup_initial_init_mm() helper 2021-07-08 11:48:21 -07:00
internal.h mm/numa: automatically generate node migration order 2021-09-03 09:58:16 -07:00
interval_tree.c mm/interval_tree: add comments to improve code readability 2021-04-30 11:20:38 -07:00
io-mapping.c mm: add a io_mapping_map_user helper 2021-04-30 11:20:39 -07:00
ioremap.c mm/ioremap: fix iomap_max_page_shift 2021-05-14 19:41:32 -07:00
khugepaged.c huge tmpfs: SGP_NOALLOC to stop collapse_file() on race 2021-09-03 09:58:12 -07:00
kmemleak.c kasan, kmemleak: reset tags when scanning block 2021-08-13 14:09:31 -10:00
ksm.c mm: KSM: fix data type 2021-09-03 09:58:18 -07:00
list_lru.c mm: vmscan: consolidate shrinker_maps handling code 2021-05-05 11:27:23 -07:00
maccess.c uaccess: add force_uaccess_{begin,end} helpers 2020-08-12 10:57:59 -07:00
madvise.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
mapping_dirty_helpers.c mm/mapping_dirty_helpers: remove double Note in kerneldoc 2021-07-01 11:06:02 -07:00
memblock.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
memcontrol.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
memfd.c Reimplement RLIMIT_MEMLOCK on top of ucounts 2021-04-30 14:14:02 -05:00
memory-failure.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
memory.c mm: fix the deadlock in finish_fault() 2021-07-23 17:43:28 -07:00
memory_hotplug.c mm/migrate: enable returning precise migrate_pages() success count 2021-09-03 09:58:16 -07:00
mempolicy.c mm/mempolicy.c: use in_task() in mempolicy_slab_node() 2021-09-03 09:58:17 -07:00
mempool.c kasan: use separate (un)poison implementation for integrated init 2021-06-04 19:32:21 +01:00
memremap.c mm/memremap.c: fix improper SPDX comment style 2021-04-30 11:20:37 -07:00
memtest.c
…
migrate.c mm/migrate: correct kernel-doc notation 2021-09-03 09:58:18 -07:00
mincore.c inode: make init and permission helpers idmapped mount aware 2021-01-24 14:27:16 +01:00
mlock.c mm: introduce memfd_secret system call to create "secret" memory areas 2021-07-08 11:48:21 -07:00
mm_init.c include/linux/page-flags-layout.h: cleanups 2021-04-30 11:20:42 -07:00
mmap.c Merge tag 'denywrite-for-5.15' of git://github.com/davidhildenbrand/linux 2021-09-04 11:35:47 -07:00
mmap_lock.c mm: mmap_lock: fix disabling preemption directly 2021-07-23 17:43:28 -07:00
mmu_gather.c mm: eliminate "expecting prototype" kernel-doc warnings 2021-04-16 16:10:36 -07:00
mmu_notifier.c mm/mmu_notifiers: ensure range_end() is paired with range_start() 2021-03-25 09:22:55 -07:00
mmzone.c mm/lru: replace pgdat lru_lock with lruvec lock 2020-12-15 14:48:04 -08:00
mprotect.c mm: device exclusive memory access 2021-07-01 11:06:03 -07:00
mremap.c mm/mremap: fix memory account on do_munmap() failure 2021-09-03 09:58:14 -07:00
msync.c mm/msync: exit early when the flags is an MS_ASYNC and start < vm_start 2021-04-30 11:20:37 -07:00
nommu.c Merge tag 'denywrite-for-5.15' of git://github.com/davidhildenbrand/linux 2021-09-04 11:35:47 -07:00
oom_kill.c mm: introduce process_mrelease system call 2021-09-03 09:58:17 -07:00
page-writeback.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
page_alloc.c mm/migrate: enable returning precise migrate_pages() success count 2021-09-03 09:58:16 -07:00
page_counter.c mm: page_counter: mitigate consequences of a page_counter underflow 2021-04-30 11:20:38 -07:00
page_ext.c mm: replace CONFIG_FLAT_NODE_MEM_MAP with CONFIG_FLATMEM 2021-06-29 10:53:55 -07:00
page_idle.c mm: page_idle_get_page() does not need lru_lock 2020-12-15 14:48:03 -08:00
page_io.c swap: fix swapfile read/write offset 2021-03-02 17:25:46 -07:00
page_isolation.c mm/page_isolation: tracing: trace all test_pages_isolated failures 2021-09-03 09:58:15 -07:00
page_owner.c mm/page_owner: constify dump_page_owner 2021-06-29 10:53:53 -07:00
page_poison.c mm: page_poison: print page info when corruption is caught 2021-04-30 11:20:36 -07:00
page_reporting.c mm/page_reporting: allow driver to specify reporting order 2021-06-29 10:53:47 -07:00
page_reporting.h mm/page_reporting: export reporting order as module parameter 2021-06-29 10:53:47 -07:00
page_vma_mapped.c mm: device exclusive memory access 2021-07-01 11:06:03 -07:00
pagewalk.c mm: pagewalk: fix walk for hugepage tables 2021-06-29 10:53:49 -07:00
percpu-internal.h Merge branch 'for-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu 2021-07-01 17:17:24 -07:00
percpu-km.c percpu: flush tlb in pcpu_reclaim_populated() 2021-07-04 18:30:17 +00:00
percpu-stats.c percpu: rework memcg accounting 2021-06-05 20:43:15 +00:00
percpu-vm.c percpu: flush tlb in pcpu_reclaim_populated() 2021-07-04 18:30:17 +00:00
percpu.c mm/percpu,c: remove obsolete comments of pcpu_chunk_populated() 2021-09-03 09:58:18 -07:00
pgalloc-track.h mm: fix typos in comments 2021-05-07 00:26:35 -07:00
pgtable-generic.c mm/thp: fix __split_huge_pmd_locked() on shmem migration entry 2021-06-16 09:24:42 -07:00
process_vm_access.c mm/process_vm_access.c: remove duplicate include 2021-05-05 11:27:27 -07:00
ptdump.c mm: ptdump: fix build failure 2021-04-16 16:10:37 -07:00
readahead.c mm: Protect operations adding pages to page cache with invalidate_lock 2021-07-13 13:14:27 +02:00
rmap.c \n 2021-08-30 10:24:50 -07:00
rodata_test.c mm/rodata_test.c: fix missing function declaration 2020-08-21 09:52:53 -07:00
secretmem.c mm/secretmem: wire up ->set_page_dirty 2021-07-23 17:43:28 -07:00
shmem.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
shuffle.c mm: eliminate "expecting prototype" kernel-doc warnings 2021-04-16 16:10:36 -07:00
shuffle.h mm/shuffle: fix section mismatch warning 2021-05-22 15:09:07 -10:00
slab.c mm: fix typos in comments 2021-05-07 00:26:35 -07:00
slab.h mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook() 2021-07-30 10:14:39 -07:00
slab_common.c Merge branch 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu 2021-07-04 12:58:33 -07:00
slob.c mm: Don't build mm_dump_obj() on CONFIG_PRINTK=n kernels 2021-03-08 14:18:46 -08:00
slub.c mm: slub: fix slub_debug disabling for list of slabs 2021-08-13 14:09:31 -10:00
sparse-vmemmap.c mm: sparsemem: split the huge PMD mapping of vmemmap pages 2021-06-30 20:47:26 -07:00
sparse.c mm: introduce memmap_alloc() to unify memory map allocation 2021-09-03 09:58:15 -07:00
swap.c mm: delete unused get_kernel_page() 2021-09-03 09:58:11 -07:00
swap_cgroup.c
…
swap_slots.c mm: Replace deprecated CPU-hotplug functions. 2021-08-28 01:46:17 +02:00
swap_state.c Revert "mm: swap: check if swap backing device is congested or not" 2021-08-20 11:31:42 -07:00
swapfile.c mm, memcg: inline swap-related functions to improve disabled memcg config 2021-09-03 09:58:12 -07:00
truncate.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
usercopy.c mm/usercopy.c: delete duplicated word 2020-08-12 10:57:58 -07:00
userfaultfd.c userfaultfd: change mmap_changing to atomic 2021-09-03 09:58:16 -07:00
util.c mm: don't allow oversized kvmalloc() calls 2021-09-02 09:47:01 -07:00
vmacache.c
…
vmalloc.c mm/vmalloc: fix wrong behavior in vread 2021-09-03 09:58:14 -07:00
vmpressure.c mm/vmpressure: replace vmpressure_to_css() with vmpressure_to_memcg() 2021-09-03 09:58:17 -07:00
vmscan.c mm, vmscan: guarantee drop_slab_node() termination 2021-09-03 09:58:17 -07:00
vmstat.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
workingset.c mm: workingset: define macro WORKINGSET_SHIFT 2021-06-30 20:47:28 -07:00
z3fold.c mm/z3fold: add kerneldoc fields for z3fold_pool 2021-07-01 11:06:03 -07:00
zbud.c mm/zbud: add kerneldoc fields for zbud_pool 2021-07-01 11:06:03 -07:00
zpool.c mm: fix typos in comments 2021-05-07 00:26:35 -07:00
zsmalloc.c mm/zsmalloc.c: improve readability for async_free_zspage() 2021-07-01 11:06:02 -07:00
zswap.c mm/zswap.c: fix two bugs in zswap_writeback_entry() 2021-06-30 20:47:31 -07:00