mm: pass mm to grab_swap_token

If a kthread happens to use get_user_pages() on an mm (as KSM does),
there's a chance that it will end up trying to read in a swap page, then
oops in grab_swap_token() because the kthread has no mm: GUP passes down
the right mm, so grab_swap_token() ought to be using it.

We have not identified a stronger case than KSM's daemon (not yet in
mainline), but the issue must have come up before, since RHEL has included
a fix for this for years (though a different fix, they just back out of
grab_swap_token if current->mm is unset: which is what we first proposed,
but using the right mm here seems more correct).

Reported-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 50da9511aa77..f46ac18ba231 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2519,7 +2519,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         delayacct_set_flag(DELAYACCT_PF_SWAPIN);
         page = lookup_swap_cache(entry);
         if (!page) {
-                grab_swap_token(); /* Contend for token _before_ read-in */
+                grab_swap_token(mm); /* Contend for token _before_ read-in */
                 page = swapin_readahead(entry,
                                         GFP_HIGHUSER_MOVABLE, vma, address);
                 if (!page) {