mm/swap_slots.c: fix race conditions in swap_slots cache init

Memory allocations can happen before the swap_slots cache initialization
is completed during cpu bring up.  If we are low on memory, we could
call get_swap_page() and access swap_slots_cache before it is fully
initialized.

Add a check in get_swap_page() for initialized swap_slots_cache to
prevent this condition.  Similar check already exists in free_swap_slot.
Also annotate the checks to indicate the likely condition.

We also added a memory barrier to make sure that the locks
initialization are done before the assignment of cache->slots and
cache->slots_ret pointers.  This ensures the assumption that it is safe
to acquire the slots cache locks and use the slots cache when the
corresponding cache->slots or cache->slots_ret pointers are non null.

[[email protected]: tidy up comment]
[[email protected]: fix spello in comment]
Link: http://lkml.kernel.org/r/65a9d0f133f63e66bba37b53b2fd0464b7cae771.1500677066.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <[email protected]>
Reported-by: Wenwei Tao <[email protected]>
Acked-by: Ying Huang <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions