diff options
author | Hugh Dickins <hughd@google.com> | 2018-12-01 01:10:16 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-12-05 21:31:57 +0300 |
commit | 7e18656c9a2c642ac8abb7b7934367fdd26f8a3f (patch) | |
tree | db30279c3d25a8b366263b7eddf4c9c0cf5cfa03 /mm/huge_memory.c | |
parent | 69697e6a61c77c8d3d7aefa1109f9bbe011eb180 (diff) | |
download | linux-7e18656c9a2c642ac8abb7b7934367fdd26f8a3f.tar.xz |
mm/huge_memory: splitting set mapping+index before unfreeze
commit 173d9d9fd3ddae84c110fea8aedf1f26af6be9ec upstream.
Huge tmpfs stress testing has occasionally hit shmem_undo_range()'s
VM_BUG_ON_PAGE(page_to_pgoff(page) != index, page).
Move the setting of mapping and index up before the page_ref_unfreeze()
in __split_huge_page_tail() to fix this: so that a page cache lookup
cannot get a reference while the tail's mapping and index are unstable.
In fact, might as well move them up before the smp_wmb(): I don't see an
actual need for that, but if I'm missing something, this way round is
safer than the other, and no less efficient.
You might argue that VM_BUG_ON_PAGE(page_to_pgoff(page) != index, page) is
misplaced, and should be left until after the trylock_page(); but left as
is has not crashed since, and gives more stringent assurance.
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261516380.2275@eggly.anvils
Fixes: e9b61f19858a5 ("thp: reintroduce split_huge_page()")
Requires: 605ca5ede764 ("mm/huge_memory.c: reorder operations in __split_huge_page_tail()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org> [4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r-- | mm/huge_memory.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index ef573d719eb4..c12b441a99f9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2373,6 +2373,12 @@ static void __split_huge_page_tail(struct page *head, int tail, (1L << PG_unevictable) | (1L << PG_dirty))); + /* ->mapping in first tail page is compound_mapcount */ + VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING, + page_tail); + page_tail->mapping = head->mapping; + page_tail->index = head->index + tail; + /* Page flags must be visible before we make the page non-compound. */ smp_wmb(); @@ -2393,12 +2399,6 @@ static void __split_huge_page_tail(struct page *head, int tail, if (page_is_idle(head)) set_page_idle(page_tail); - /* ->mapping in first tail page is compound_mapcount */ - VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING, - page_tail); - page_tail->mapping = head->mapping; - - page_tail->index = head->index + tail; page_cpupid_xchg_last(page_tail, page_cpupid_last(head)); /* |