shmem_swapin_page()'s swap_free() has occasionally been generating
"_swap_info_get: Unused swap offset entry" messages. Usually that's
no worse than noise; but perhaps it indicates a worse case, when we
might there be freeing swap already reused by others.
The multi-index xas_find_conflict() loop in shmem_add_to_page_cache()
did not allow for entry found NULL when expected to be non-NULL, so did
not catch that race when the swap has already been freed.
The loop would not actually catch a realistic conflict which the single
check does not catch, so revert it back to the single check.
Fixes: 3103f9a51dd0 ("mm: Use multi-index entries in the page cache")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/shmem.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- hughd2/mm/shmem.c
+++ hughd3/mm/shmem.c
@@ -727,9 +727,8 @@ static int shmem_add_to_page_cache(struc
do {
void *entry;
xas_lock_irq(&xas);
- while ((entry = xas_find_conflict(&xas)) != NULL) {
- if (entry == expected)
- continue;
+ entry = xas_find_conflict(&xas);
+ if (entry != expected) {
xas_set_err(&xas, -EEXIST);
goto unlock;
}
