mm: copy over oom_adj value at fork time

mm: copy over oom_adj value at fork time

Fix a post-2.6.31 regression which was introduced by
2ff05b2b4eac2e63d345fc731ea151a060247f53 ("oom: move oom_adj value from
task_struct to mm_struct").

After moving the oom_adj value from the task struct to the mm_struct, the
oom_adj value was no longer properly inherited by child processes.

Copying over the oom_adj value at fork time fixes that bug.

[[email protected]: test for current->mm before dereferencing it]
Signed-off-by: Rik van Riel <[email protected]>
Reported-by: Paul Menage <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Acked-by: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>