From: "Huang\, Ying" <ying.huang@intel.com>
To: Chen Wandun <chenwandun@huawei.com>
Cc: <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [Question] Is there race between swapoff and swapout
Date: Thu, 24 Oct 2019 16:51:08 +0800 [thread overview]
Message-ID: <87sgnih6gz.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <8860e8b1-7bad-0b4a-60d1-4893973b9cb2@huawei.com> (Chen Wandun's message of "Mon, 14 Oct 2019 21:22:35 +0800")
Chen Wandun <chenwandun@huawei.com> writes:
> I analysied the code about swapoff and swapout, and I suspected there may be a race.
> The kernel version is 4.14 stable.
>
> CPU0 CPU1
> swapoff swap out
> add_to_swap
> get_swap_page
> ...... get_swap_pages
> spin_lock(&swap_avail_lock)
> get swap_info_struct
> spin_unlock(&swap_avail_lock)
> spin_lock(&swap_avail_lock)
> __def_from_avail_list(swap_info_struct)
> spin_unlock(&swap_avail_lock) ......
> try_to_unuse // unuse all slot
> /* get a free slot from swap_info_struct,
> * and write data to slot later
> */
> scan_swap_map_slots
> free swap_info_struct
> .......
>
>
> If CPU1 get the swap_info_struct first, then CPU0 delete it from list and
> unuse all slot in swap_info_struct, before CPU0 free swap_info_struct CPU1
> call scan_swap_map_slots to alloc a free slot.
>
> I am not sure the analysis above is correct,
> Please let me know if there is any mistake
SWP_WRITEOK will be cleared during swapoff, and it is checked during
swap slots allocation.
Best Regards,
Huang, Ying
> Thanks
> ChenWandun
prev parent reply other threads:[~2019-10-24 8:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-14 13:22 [Question] Is there race between swapoff and swapout Chen Wandun
2019-10-24 8:51 ` Huang, Ying [this message]
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