Commit 2efa33fc authored Jun 28, 2021 by Miaohe Lin Committed by Linus Torvalds Jun 29, 2021

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@huawei.com


Fixes: 8fd2e0b5 ("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>

parent 5c046235

mm/shmem.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -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 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index,
		put_page(page);
		}

		if (si)
		put_swap_device(si);

		return error;
		}