linux-kernel - Re: [PATCH 0/5] close various race windows for swap

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Date:   Thu, 8 Apr 2021 20:25:17 +0530
From:   riteshh <riteshh@...ux.ibm.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org, mhocko@...e.com,
        iamjoonsoo.kim@....com, vbabka@...e.cz, alex.shi@...ux.alibaba.com,
        willy@...radead.org, minchan@...nel.org, richard.weiyang@...il.com,
        ying.huang@...el.com, hughd@...gle.com, tim.c.chen@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/5] close various race windows for swap

On 21/04/08 09:08AM, Miaohe Lin wrote:
> 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 the rest of the patches use this to close various
> race windows. More details can be found in the respective changelogs.
> Thanks!
>
> Miaohe Lin (5):
>   mm/swapfile: add percpu_ref support for swap
>   swap: fix do_swap_page() race with swapoff
>   mm/swap_state: fix get_shadow_from_swap_cache() race with swapoff
>   mm/swap_state: fix potential faulted in race in swap_ra_info()
>   mm/swap_state: fix swap_cluster_readahead() race with swapoff

Somehow I see Patch-1 and Patch-2 are missing on linux-mm[1].
Also I wanted to ask if you have a way to trigger this in a more controlled
environment (consistently)?

[1]: https://patchwork.kernel.org/project/linux-mm/cover/20210408130820.48233-1-linmiaohe@huawei.com/

-ritesh

>
>  include/linux/swap.h |  4 +++-
>  mm/memory.c          | 10 +++++++++
>  mm/swap_state.c      | 33 +++++++++++++++++++++--------
>  mm/swapfile.c        | 50 +++++++++++++++++++++++++++-----------------
>  4 files changed, 68 insertions(+), 29 deletions(-)
>
> --
> 2.19.1
>
>