| Message ID | 20210420133048.6773-5-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 > ----- ----- > shmem_swapin > swap_cluster_readahead > if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) { > swapoff > percpu_ref_kill(&p->users) > synchronize_rcu() > wait_for_completion I don't think the above 3 lines are relevant for the race. > .. > si->swap_file = NULL; > struct inode *inode = si->swap_file->f_mapping->host;[oops!] > > Close this race window by using get/put_swap_device() to guard against > concurrent swapoff. > > Fixes: 8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not") > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/shmem.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 26c76b13ad23..936ba5595297 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1492,15 +1492,21 @@ static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma) > static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp, > struct shmem_inode_info *info, pgoff_t index) > { > + struct swap_info_struct *si; > struct vm_area_struct pvma; > struct page *page; > struct vm_fault vmf = { > .vma = &pvma, > }; > > + /* Prevent swapoff from happening to us. */ > + si = get_swap_device(swap); Better to put get/put_swap_device() in shmem_swapin_page(), that make it possible for us to remove get/put_swap_device() in lookup_swap_cache(). Best Regards, Huang, Ying > + if (unlikely(!si)) > + return NULL; > shmem_pseudo_vma_init(&pvma, info, index); > page = swap_cluster_readahead(swap, gfp, &vmf); > shmem_pseudo_vma_destroy(&pvma); > + put_swap_device(si); > > return page; > }
diff --git a/mm/shmem.c b/mm/shmem.c index 26c76b13ad23..936ba5595297 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1492,15 +1492,21 @@ static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma) static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp, struct shmem_inode_info *info, pgoff_t index) { + struct swap_info_struct *si; struct vm_area_struct pvma; struct page *page; struct vm_fault vmf = { .vma = &pvma, }; + /* Prevent swapoff from happening to us. */ + si = get_swap_device(swap); + if (unlikely(!si)) + return NULL; shmem_pseudo_vma_init(&pvma, info, index); page = swap_cluster_readahead(swap, gfp, &vmf); shmem_pseudo_vma_destroy(&pvma); + put_swap_device(si); return page; }
When I was investigating the swap code, I found the below possible race window: CPU 1 CPU 2 ----- ----- shmem_swapin swap_cluster_readahead if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) { swapoff percpu_ref_kill(&p->users) synchronize_rcu() wait_for_completion .. si->swap_file = NULL; struct inode *inode = si->swap_file->f_mapping->host;[oops!] Close this race window by using get/put_swap_device() to guard against concurrent swapoff. Fixes: 8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not") Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/shmem.c | 6 ++++++ 1 file changed, 6 insertions(+)