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, 6 insertions, 6 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index c88b36665f79..7c15334f3ff2 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -298,8 +298,8 @@ extern int try_to_free_swap(struct page *);
 struct backing_dev_info;
 
 /* linux/mm/thrash.c */
-extern struct mm_struct * swap_token_mm;
-extern void grab_swap_token(void);
+extern struct mm_struct *swap_token_mm;
+extern void grab_swap_token(struct mm_struct *);
 extern void __put_swap_token(struct mm_struct *);
 
 static inline int has_swap_token(struct mm_struct *mm)
@@ -419,10 +419,10 @@ static inline swp_entry_t get_swap_page(void)
 }
 
 /* linux/mm/thrash.c */
-#define put_swap_token(x) do { } while(0)
-#define grab_swap_token()  do { } while(0)
-#define has_swap_token(x) 0
-#define disable_swap_token() do { } while(0)
+#define put_swap_token(mm)      do { } while (0)
+#define grab_swap_token(mm)     do { } while (0)
+#define has_swap_token(mm)      0
+#define disable_swap_token()    do { } while (0)
 
 static inline void
 mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent)