mm: pass mm to grab_swap_token
authorHugh Dickins <hugh.dickins@tiscali.co.uk>
Tue, 23 Jun 2009 19:36:58 +0000 (12:36 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 23 Jun 2009 19:50:05 +0000 (12:50 -0700)
commita5c9b696ec109bb54d547fdb437a7a0c2d514670
treec97533e38359a2e731bcc2c65f063a27f4f629e6
parent626f380d0b264a1e40237f5a2a3dffc5d14f256e
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>
include/linux/swap.h
mm/memory.c
mm/thrash.c