ipc/sem.c: use READ_ONCE()/WRITE_ONCE() for use_global_lock

The patch solves three weaknesses in ipc/sem.c:

1) The initial read of use_global_lock in sem_lock() is an intentional
   race.  KCSAN detects these accesses and prints a warning.

2) The code assumes that plain C read/writes are not mangled by the CPU
   or the compiler.

3) The comment it sysvipc_sem_proc_show() was hard to understand: The
   rest of the comments in ipc/sem.c speaks about sem_perm.lock, and
   suddenly this function speaks about ipc_lock_object().

To solve 1) and 2), use READ_ONCE()/WRITE_ONCE().  Plain C reads are used
in code that owns sma->sem_perm.lock.

The comment is updated to solve 3)

[[email protected]: use READ_ONCE()/WRITE_ONCE() for use_global_lock]
  Link: https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Manfred Spraul <[email protected]>
Reviewed-by: Paul E. McKenney <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions