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mm: pass mm to grab_swap_token

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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>
This commit is contained in:
Hugh Dickins 2009-06-23 12:36:58 -07:00 • committed by Linus Torvalds
commit a5c9b696ec
3 changed files with 22 additions and 24 deletions
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12
include/linux/swap.h
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@ -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)