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/[email protected]
Fixes: 8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not")
Signed-off-by: Miaohe Lin <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Cc: Dennis Zhou <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Alex Shi <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Yu Zhao <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/shmem.c b/mm/shmem.c
index 5d46611cba8dca00882a9c2799288f93127fca48..53f21016608e3c63f102fcab98ed6f422c1bdd67 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1696,7 +1696,8 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index,
        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 inode *inode, pgoff_t index,
        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 inode *inode, pgoff_t index,
        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;
 }