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
..
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.
Link: https://lkml.kernel.org/r/20210426123316.806267-5-linmiaohe@huawei.com
Fixes:
8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
struct address_space *mapping = inode->i_mapping;
struct shmem_inode_info *info = SHMEM_I(inode);
struct mm_struct *charge_mm = vma ? vma->vm_mm : current->mm;
- struct page *page;
+ struct swap_info_struct *si;
+ struct page *page = NULL;
swp_entry_t swap;
int error;
swap = radix_to_swp_entry(*pagep);
*pagep = NULL;
+ /* Prevent swapoff from happening to us. */
+ si = get_swap_device(swap);
+ if (!si) {
+ error = EINVAL;
+ goto failed;
+ }
/* Look it up and read it in.. */
page = lookup_swap_cache(swap, NULL, 0);
if (!page) {
swap_free(swap);
*pagep = page;
+ if (si)
+ put_swap_device(si);
return 0;
failed:
if (!shmem_confirm_swap(mapping, index, swap))
put_page(page);
}
+ if (si)
+ put_swap_device(si);
+
return error;
}