From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Subject: mm/shmem: fix shmem_swapin() race with swapoff
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@xxxxxxxxxx
Fixes: 8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Alex Shi <alexs@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
--- a/mm/shmem.c~mm-shmem-fix-shmem_swapin-race-with-swapoff
+++ a/mm/shmem.c
@@ -1696,7 +1696,8 @@ static int shmem_swapin_page(struct inod
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;
@@ -1704,6 +1705,12 @@ static int shmem_swapin_page(struct inod
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) {
@@ -1765,6 +1772,8 @@ static int shmem_swapin_page(struct inod
swap_free(swap);
*pagep = page;
+ if (si)
+ put_swap_device(si);
return 0;
failed:
if (!shmem_confirm_swap(mapping, index, swap))
@@ -1775,6 +1784,9 @@ unlock:
put_page(page);
}
+ if (si)
+ put_swap_device(si);
+
return error;
}
_
