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)
[manfred@colorfullife.com: use READ_ONCE()/WRITE_ONCE() for use_global_lock]
Link: https://lkml.kernel.org/r/20210627161919.3196-3-manfred@colorfullife.com
Link: https://lkml.kernel.org/r/20210514175319.12195-1-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: <1vier1@web.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed