Re: [PATCH net] rds: Make sure updates to cp_send_gen can be observed

Santosh Shilimkar
2017-07-20T16:50:03Z

On 7/20/2017 3:28 AM, Håkon Bugge wrote:
> cp->cp_send_gen is treated as a normal variable, although it may be
> used by different threads.
>
> This is fixed by using {READ,WRITE}_ONCE when it is incremented and
> READ_ONCE when it is read outside the {acquire,release}_in_xmit
> protection.
>
There is explicit memory barrier before the value is read outside
the {acquire,release}_in_xmit so it takes care of load/store sync.

> Normative reference from the Linux-Kernel Memory Model:
>
> Loads from and stores to shared (but non-atomic) variables should
> be protected with the READ_ONCE(), WRITE_ONCE(), and
> ACCESS_ONCE().
>
> Clause 5.1.2.4/25 in the C standard is also relevant.
>
> Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
> Reviewed-by: Knut Omang <knut.omang@oracle.com>
> ---
Having said that, {READ,WRITE}_ONCE usages seems to make
it clear and explicit. So its fine with me.

Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>