ipc/sem.c: fully initialize sem_array before making it visible

ipc/sem.c: fully initialize sem_array before making it visible

ipc_addid() makes a new ipc identifier visible to everyone.  New objects
start as locked, so that the caller can complete the initialization
after the call.  Within struct sem_array, at least sma->sem_base and
sma->sem_nsems are accessed without any locks, therefore this approach
doesn't work.

Thus: Move the ipc_addid() to the end of the initialization.

Signed-off-by: Manfred Spraul <[email protected]>
Reported-by: Rik van Riel <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Acked-by: Rafael Aquini <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>