linux-kernel - [PATCH v6 0/4] close various race windows for swap

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Date:   Mon, 26 Apr 2021 20:33:12 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <ying.huang@...el.com>, <dennis@...nel.org>,
        <tim.c.chen@...ux.intel.com>, <hughd@...gle.com>,
        <hannes@...xchg.org>, <mhocko@...e.com>, <iamjoonsoo.kim@....com>,
        <alexs@...nel.org>, <willy@...radead.org>, <minchan@...nel.org>,
        <richard.weiyang@...il.com>, <shy828301@...il.com>,
        <david@...hat.com>, <yuzhao@...gle.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH v6 0/4] close various race windows for swap

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!

v5->v6:
  collect Reviewed-by tag
  fix page uninitialized in failed case per Yu Zhao

v4->v5:
  collect Reviewed-by tag
  do put_swap_device() before returning from the function per Huang, Ying

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           | 14 +++++++-
 mm/swap_state.c      |  6 ----
 mm/swapfile.c        | 79 +++++++++++++++++++++++++++-----------------
 5 files changed, 83 insertions(+), 41 deletions(-)

-- 
2.23.0