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Re: [PATCH] ipc/sem.c: Update/correct memory barriers

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On 08/09, Manfred Spraul wrote:
>
>  /*
> + * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
> + * are only control barriers.
> + * The code must pair with spin_unlock(&sem->lock) or
> + * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient.
> + *
> + * smp_rmb() is sufficient, as writes cannot pass the control barrier.
> + */
> +#define ipc_smp_acquire__after_spin_is_unlocked()	smp_rmb()

Agreed.



But to remind, this can have more users. In particular, task_work_run()
which currently does mb() after spin_unlock_wait().

Can someone suggest a good "generic" name for this helper so that we can
move it into include/linux/spinlock.h?

Oleg.

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[PATCH] ipc/sem.c: Update/correct memory barriers Manfred Spraul <manfred@colorfullife.com> - 2015-08-09 20:00 +0200
  Re: [PATCH] ipc/sem.c: Update/correct memory barriers Peter Zijlstra <peterz@infradead.org> - 2015-08-10 10:20 +0200
  Re: [PATCH] ipc/sem.c: Update/correct memory barriers Oleg Nesterov <oleg@redhat.com> - 2015-08-12 15:40 +0200

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