Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Miaohe Lin <> | Subject | [PATCH v5 2/4] swap: fix do_swap_page() race with swapoff | Date | Sun, 25 Apr 2021 17:54:17 +0800 |
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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@intel.com> (auto build test ERROR) Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- 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; } -- 2.23.0
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