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Message-ID: <877dkrxdqj.fsf@yhuang6-desk1.ccr.corp.intel.com>
Date: Sun, 25 Apr 2021 11:08:36 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Miaohe Lin <linmiaohe@...wei.com>
Cc: <akpm@...ux-foundation.org>, <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>, <linux-kernel@...r.kernel.org>,
<linux-mm@...ck.org>
Subject: Re: [PATCH v4 2/4] swap: fix do_swap_page() race with swapoff
Miaohe Lin <linmiaohe@...wei.com> writes:
> When I was investigating the swap code, I found the below possible race
> window:
>
> CPU 1 CPU 2
> ----- -----
> do_swap_page
> if (data_race(si->flags & SWP_SYNCHRONOUS_IO)
> swap_readpage
> if (data_race(sis->flags & SWP_FS_OPS)) {
> swapoff
> ..
> p->swap_file = NULL;
> ..
> struct file *swap_file = sis->swap_file;
> struct address_space *mapping = swap_file->f_mapping;[oops!]
>
> Note that for the pages that are swapped in through swap cache, this isn't
> an issue. Because the page is locked, and the swap entry will be marked
> with SWAP_HAS_CACHE, so swapoff() can not proceed until the page has been
> unlocked.
>
> Fix this race by using get/put_swap_device() to guard against concurrent
> swapoff.
>
> Fixes: 0bcac06f27d7 ("mm,swap: skip swapcache for swapin of synchronous device")
> Reported-by: kernel test robot <lkp@...el.com> (auto build test ERROR)
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
Best Regards,
Huang, Ying
> ---
> include/linux/swap.h | 9 +++++++++
> mm/memory.c | 11 +++++++++--
> 2 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index c9e7fea10b83..46d51d058d05 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -527,6 +527,15 @@ static inline struct swap_info_struct *swp_swap_info(swp_entry_t entry)
> return NULL;
> }
>
> +static inline struct swap_info_struct *get_swap_device(swp_entry_t entry)
> +{
> + return NULL;
> +}
> +
> +static inline void put_swap_device(struct swap_info_struct *si)
> +{
> +}
> +
> #define swap_address_space(entry) (NULL)
> #define get_nr_swap_pages() 0L
> #define total_swap_pages 0L
> diff --git a/mm/memory.c b/mm/memory.c
> index 27014c3bde9f..39c910678387 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3311,6 +3311,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
> struct page *page = NULL, *swapcache;
> + struct swap_info_struct *si = NULL;
> swp_entry_t entry;
> pte_t pte;
> int locked;
> @@ -3338,14 +3339,16 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> goto out;
> }
>
> + /* Prevent swapoff from happening to us. */
> + si = get_swap_device(entry);
> + if (unlikely(!si))
> + goto out;
>
> delayacct_set_flag(current, DELAYACCT_PF_SWAPIN);
> page = lookup_swap_cache(entry, vma, vmf->address);
> swapcache = page;
>
> if (!page) {
> - struct swap_info_struct *si = swp_swap_info(entry);
> -
> if (data_race(si->flags & SWP_SYNCHRONOUS_IO) &&
> __swap_count(entry) == 1) {
> /* skip swapcache */
> @@ -3514,6 +3517,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> unlock:
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> out:
> + if (si)
> + put_swap_device(si);
> return ret;
> out_nomap:
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> @@ -3525,6 +3530,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> unlock_page(swapcache);
> put_page(swapcache);
> }
> + if (si)
> + put_swap_device(si);
> return ret;
> }
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