[PATCH v4 0/4] close various race windows for swap

[Miaohe Lin]

Hi all,
When I was investigating the swap code, I found some possible race
windows. This series aims to fix all these races. But using current
get/put_swap_device() to guard against concurrent swapoff for
swap_readpage() looks terrible because swap_readpage() may take really
long time. And to reduce the performance overhead on the hot-path as
much as possible, it appears we can use the percpu_ref to close this
race window(as suggested by Huang, Ying). The patch 1 adds percpu_ref
support for swap and most of the remaining patches try to use this to
close various race windows. More details can be found in the respective
changelogs. Thanks!

v3->v4:
  some commit log and comment enhance per Huang, Ying
  put get/put_swap_device() in shmem_swapin_page() per Huang, Ying
  collect Reviewed-by tag

v2->v3:
  some commit log and comment enhance per Huang, Ying
  remove ref_initialized field
  squash PATCH 1-2

v1->v2:
  reorganize the patch-2/5
  various enhance and fixup per Huang, Ying
  Many thanks for the comments of Huang, Ying, Dennis Zhou and Tim Chen.

Miaohe Lin (4):
  mm/swapfile: use percpu_ref to serialize against concurrent swapoff
  swap: fix do_swap_page() race with swapoff
  mm/swap: remove confusing checking for non_swap_entry() in
    swap_ra_info()
  mm/shmem: fix shmem_swapin() race with swapoff

 include/linux/swap.h | 14 ++++++--
 mm/memory.c          | 11 ++++--
 mm/shmem.c           | 11 ++++++
 mm/swap_state.c      |  6 ----
 mm/swapfile.c        | 79 +++++++++++++++++++++++++++-----------------
 5 files changed, 81 insertions(+), 40 deletions(-)

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2.19.1