mm: bugfix: set current->reclaim_state to NULL while returning from kswapd()

mm: bugfix: set current->reclaim_state to NULL while returning from kswapd()

In kswapd(), set current->reclaim_state to NULL before returning, as
current->reclaim_state holds reference to variable on kswapd()'s stack.

In rare cases, while returning from kswapd() during memory offlining,
__free_slab() and freepages() can access the dangling pointer of
current->reclaim_state.

Signed-off-by: Takamori Yamaguchi <[email protected]>
Signed-off-by: Aaditya Kumar <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>