Revert "mm/shmem: fix shmem_swapin() race with swapoff"

Due to the change about how block layer detects congestion the
justification of commit 8fd2e0b505d1 ("mm: swap: check if swap backing
device is congested or not") doesn't stand anymore, so the commit could
be just reverted in order to solve the race reported by commit
2efa33fc7f6e ("mm/shmem: fix shmem_swapin() race with swapoff"), so the
fix commit could be just reverted as well.

And that fix is also kind of buggy as discussed by [1] and [2].

[1] https://lore.kernel.org/linux-mm/24187e5e-069-9f3f-cefe-39ac70783753@google.com/
[2] https://lore.kernel.org/linux-mm/e82380b9-3ad4-4a52-be50-6d45c7f2b5da@google.com/

Link: https://lkml.kernel.org/r/20210810202936.2672-2-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Suggested-by: Hugh Dickins <hughd@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index 70d9ce2..dacda74 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1696,8 +1696,7 @@ 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 : NULL;
-       struct swap_info_struct *si;
-       struct page *page = NULL;
+       struct page *page;
        swp_entry_t swap;
        int error;
 
@@ -1705,12 +1704,6 @@ 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) {
@@ -1772,8 +1765,6 @@ 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))
@@ -1784,9 +1775,6 @@ unlock:
                put_page(page);
        }
 
-       if (si)
-               put_swap_device(si);
-
        return error;
 }