Message ID | 20210425023806.3537283-3-linmiaohe@huawei.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | close various race windows for swap | expand |
Miaohe Lin <linmiaohe@huawei.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@intel.com> (auto build test ERROR) > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.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; > }
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; }
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) Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- include/linux/swap.h | 9 +++++++++ mm/memory.c | 11 +++++++++-- 2 files changed, 18 insertions(+), 2 deletions(-)