kernel_optimize_test/mm
Linus Torvalds be068f2903 mm: fix misplaced unlock_page in do_wp_page()
Commit 09854ba94c ("mm: do_wp_page() simplification") reorganized all
the code around the page re-use vs copy, but in the process also moved
the final unlock_page() around to after the wp_page_reuse() call.

That normally doesn't matter - but it means that the unlock_page() is
now done after releasing the page table lock.  Again, not a big deal,
you'd think.

But it turns out that it's very wrong indeed, because once we've
released the page table lock, we've basically lost our only reference to
the page - the page tables - and it could now be free'd at any time.  We
do hold the mmap_sem, so no actual unmap() can happen, but madvise can
come in and a MADV_DONTNEED will zap the page range - and free the page.

So now the page may be free'd just as we're unlocking it, which in turn
will usually trigger a "Bad page state" error in the freeing path.  To
make matters more confusing, by the time the debug code prints out the
page state, the unlock has typically completed and everything looks fine
again.

This all doesn't happen in any normal situations, but it does trigger
with the dirtyc0w_child LTP test.  And it seems to trigger much more
easily (but not expclusively) on s390 than elsewhere, probably because
s390 doesn't do the "batch pages up for freeing after the TLB flush"
that gives the unlock_page() more time to complete and makes the race
harder to hit.

Fixes: 09854ba94c ("mm: do_wp_page() simplification")
Link: https://lore.kernel.org/lkml/a46e9bbef2ed4e17778f5615e818526ef848d791.camel@redhat.com/
Link: https://lore.kernel.org/linux-mm/c41149a8-211e-390b-af1d-d5eee690fecb@linux.alibaba.com/
Reported-by: Qian Cai <cai@redhat.com>
Reported-by: Alex Shi <alex.shi@linux.alibaba.com>
Bisected-and-analyzed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Tested-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-24 08:41:32 -07:00
..
kasan Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
backing-dev.c writeback: remove struct bdi_writeback_congested 2020-07-08 17:05:53 -06:00
balloon_compaction.c
cleancache.c
cma_debug.c debugfs: make sure we can remove u32_array files cleanly 2020-07-10 13:54:00 -07:00
cma.c cma: don't quit at first error when activating reserved areas 2020-08-12 10:57:57 -07:00
cma.h mm: cma: fix the name of CMA areas 2020-08-12 10:57:57 -07:00
compaction.c mm: replace hpage_nr_pages with thp_nr_pages 2020-08-14 19:56:56 -07:00
debug_page_ref.c
debug_vm_pgtable.c Documentation/mm: add descriptions for arch page table helpers 2020-08-07 11:33:23 -07:00
debug.c mm, dump_page: do not crash with bad compound_mapcount() 2020-08-07 11:33:23 -07:00
dmapool.c
early_ioremap.c
fadvise.c
failslab.c
filemap.c mm: fix wake_page_function() comment typos 2020-09-20 10:38:47 -07:00
frame_vector.c mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
frontswap.c mm/frontswap: mark various intentional data races 2020-08-14 19:56:56 -07:00
gup_benchmark.c
gup.c Merge branch 'simplify-do_wp_page' 2020-09-04 09:31:54 -07:00
highmem.c
hmm.c mm: do page fault accounting in handle_mm_fault 2020-08-12 10:58:02 -07:00
huge_memory.c mm/thp: fix __split_huge_pmd_locked() for migration PMD 2020-09-19 13:13:38 -07:00
hugetlb_cgroup.c hugetlb_cgroup: convert comma to semicolon 2020-08-21 09:52:52 -07:00
hugetlb.c mm/hugetlb: fix a race between hugetlb sysctl handlers 2020-09-05 12:14:30 -07:00
hwpoison-inject.c
init-mm.c mmap locking API: add MMAP_LOCK_INITIALIZER 2020-06-09 09:39:14 -07:00
internal.h mm: replace hpage_nr_pages with thp_nr_pages 2020-08-14 19:56:56 -07:00
interval_tree.c
ioremap.c mm: move p?d_alloc_track to separate header file 2020-08-07 11:33:26 -07:00
Kconfig mm/sparse: cleanup the code surrounding memory_present() 2020-08-07 11:33:27 -07:00
Kconfig.debug treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
khugepaged.c mm/khugepaged.c: fix khugepaged's request size in collapse_file 2020-09-05 12:14:30 -07:00
kmemleak-test.c
kmemleak.c mm/kmemleak: silence KCSAN splats in checksum 2020-08-14 19:56:56 -07:00
ksm.c ksm: reinstate memcg charge on copied pages 2020-09-19 13:13:38 -07:00
list_lru.c mm/list_lru: fix a data race in list_lru_count_one 2020-08-14 19:56:57 -07:00
maccess.c uaccess: add force_uaccess_{begin,end} helpers 2020-08-12 10:57:59 -07:00
madvise.c mm: madvise: fix vma user-after-free 2020-09-05 12:14:29 -07:00
Makefile mm: move lib/ioremap.c to mm/ 2020-08-07 11:33:26 -07:00
mapping_dirty_helpers.c
memblock.c mm/memblock: expose only miminal interface to add/walk physmem 2020-07-10 15:08:09 +02:00
memcontrol.c memcg: fix use-after-free in uncharge_batch 2020-09-05 12:14:29 -07:00
memfd.c
memory_hotplug.c mm/memory_hotplug: drain per-cpu pages again during memory offline 2020-09-19 13:13:39 -07:00
memory-failure.c mm/migrate: introduce a standard migration target allocation function 2020-08-12 10:58:02 -07:00
memory.c mm: fix misplaced unlock_page in do_wp_page() 2020-09-24 08:41:32 -07:00
mempolicy.c mm: replace hpage_nr_pages with thp_nr_pages 2020-08-14 19:56:56 -07:00
mempool.c mm/mempool: fix a data race in mempool_free() 2020-08-14 19:56:57 -07:00
memremap.c memremap: rename MEMORY_DEVICE_DEVDAX to MEMORY_DEVICE_GENERIC 2020-09-04 09:59:59 +02:00
memtest.c
migrate.c mm: migration of hugetlbfs page skip memcg 2020-09-19 13:13:38 -07:00
mincore.c mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
mlock.c mlock: fix unevictable_pgs event counts on THP 2020-09-19 13:13:38 -07:00
mm_init.c mm: adjust vm_committed_as_batch according to vm overcommit policy 2020-08-07 11:33:26 -07:00
mmap.c mm: remove unnecessary wrapper function do_mmap_pgoff() 2020-08-07 11:33:27 -07:00
mmu_gather.c mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
mmu_notifier.c mm: mmu_notifier: fix and extend kerneldoc 2020-08-12 10:57:57 -07:00
mmzone.c
mprotect.c mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
mremap.c mm/mremap: start addresses are properly aligned 2020-08-07 11:33:27 -07:00
msync.c mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
nommu.c mm/nommu.c: delete duplicated words 2020-08-12 10:57:58 -07:00
oom_kill.c mm, oom: show process exiting information in __oom_kill_process() 2020-08-12 10:57:56 -07:00
page_alloc.c mm, page_alloc: fix core hung in free_pcppages_bulk() 2020-08-21 09:52:53 -07:00
page_counter.c mm/page_counter: fix various data races at memsw 2020-08-14 19:56:57 -07:00
page_ext.c
page_idle.c
page_io.c mm/page_io: mark various intentional data races 2020-08-14 19:56:56 -07:00
page_isolation.c mm/memory_hotplug: drain per-cpu pages again during memory offline 2020-09-19 13:13:39 -07:00
page_owner.c
page_poison.c
page_reporting.c
page_reporting.h
page_vma_mapped.c mm: replace hpage_nr_pages with thp_nr_pages 2020-08-14 19:56:56 -07:00
page-writeback.c mm: remove vm_total_pages 2020-08-07 11:33:28 -07:00
pagewalk.c mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
percpu-internal.h mm: memcg/percpu: account percpu memory to memory cgroups 2020-08-12 10:57:55 -07:00
percpu-km.c mm: memcg/percpu: account percpu memory to memory cgroups 2020-08-12 10:57:55 -07:00
percpu-stats.c mm: memcg/percpu: account percpu memory to memory cgroups 2020-08-12 10:57:55 -07:00
percpu-vm.c mm: memcg/percpu: account percpu memory to memory cgroups 2020-08-12 10:57:55 -07:00
percpu.c percpu: fix first chunk size calculation for populated bitmap 2020-09-17 17:34:39 +00:00
pgalloc-track.h mm: move p?d_alloc_track to separate header file 2020-08-07 11:33:26 -07:00
pgtable-generic.c
process_vm_access.c mm/gup: remove task_struct pointer for all gup code 2020-08-12 10:58:04 -07:00
ptdump.c mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
readahead.c
rmap.c mm/rmap: fixup copying of soft dirty and uffd ptes 2020-09-05 12:14:30 -07:00
rodata_test.c mm/rodata_test.c: fix missing function declaration 2020-08-21 09:52:53 -07:00
shmem.c tmpfs: restore functionality of nr_inodes=0 2020-09-19 13:13:38 -07:00
shuffle.c mm/shuffle: remove dynamic reconfiguration 2020-08-07 11:33:29 -07:00
shuffle.h mm/shuffle: remove dynamic reconfiguration 2020-08-07 11:33:29 -07:00
slab_common.c mm/slab_common.c: delete duplicated word 2020-08-12 10:57:58 -07:00
slab.c mm: slab: rename (un)charge_slab_page() to (un)account_slab_page() 2020-08-07 11:33:25 -07:00
slab.h mm: slab: rename (un)charge_slab_page() to (un)account_slab_page() 2020-08-07 11:33:25 -07:00
slob.c mm: memcg: convert vmstat slab counters to bytes 2020-08-07 11:33:24 -07:00
slub.c mm: slub: fix conversion of freelist_corrupted() 2020-09-05 12:14:29 -07:00
sparse-vmemmap.c mm/sparse: only sub-section aligned range would be populated 2020-08-07 11:33:27 -07:00
sparse.c mm/sparse: cleanup the code surrounding memory_present() 2020-08-07 11:33:27 -07:00
swap_cgroup.c
swap_slots.c mm/swap_slots.c: remove redundant check for swap_slot_cache_initialized 2020-08-07 11:33:24 -07:00
swap_state.c mm/swap_state: mark various intentional data races 2020-08-14 19:56:57 -07:00
swap.c mlock: fix unevictable_pgs event counts on THP 2020-09-19 13:13:38 -07:00
swapfile.c mm/swapfile: fix and annotate various data races 2020-08-14 19:56:57 -07:00
truncate.c
usercopy.c mm/usercopy.c: delete duplicated word 2020-08-12 10:57:58 -07:00
userfaultfd.c mm/vmscan: protect the workingset on anonymous LRU 2020-08-12 10:57:55 -07:00
util.c mm: remove unnecessary wrapper function do_mmap_pgoff() 2020-08-07 11:33:27 -07:00
vmacache.c kernel: better document the use_mm/unuse_mm API contract 2020-06-10 19:14:18 -07:00
vmalloc.c mm/vunmap: add cond_resched() in vunmap_pmd_range 2020-08-21 09:52:53 -07:00
vmpressure.c
vmscan.c mm: fix check_move_unevictable_pages() on THP 2020-09-19 13:13:38 -07:00
vmstat.c Merge branch 'simplify-do_wp_page' 2020-09-04 09:31:54 -07:00
workingset.c mm: replace hpage_nr_pages with thp_nr_pages 2020-08-14 19:56:56 -07:00
z3fold.c
zbud.c
zpool.c mm/zpool.c: delete duplicated word and fix grammar 2020-08-12 10:57:58 -07:00
zsmalloc.c mm/zsmalloc.c: fix duplicated words 2020-08-12 10:57:58 -07:00
zswap.c