Re: [PATCH rcu] srcu: Guarantee non-negative return value from srcu_read_lock()
From: Alan Huang
Date: Wed Oct 23 2024 - 03:00:48 EST
On Oct 22, 2024, at 22:26, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
>
> On Tue, Oct 22, 2024 at 12:13:12AM -0700, Christoph Hellwig wrote:
>> On Tue, Oct 22, 2024 at 09:10:18AM +0200, Peter Zijlstra wrote:
>>> Ah, well, the thing that got us here is that we (Andrii and me) wanted
>>> to use -1 as an 'invalid' value to indicate SRCU is not currently in
>>> use.
>>>
>>> So it all being int is really rather convenient :-)
>>
>> Then please document that use. Maybe even with a symolic name for
>> -1 that clearly describes these uses.
>
> Would this work?
>
> #define SRCU_INVALID_INDEX -1
Is there any similar guarantee of the return value of get_state_synchronize_rcu
or start_poll_synchronize_rcu, like invalid value?
>
> Whatever the name, maybe Peter and Andrii define this under #ifndef
> right now, and we get it into include/linux/srcu.h over time.
>
> Or is there a better way? Or name, for that matter.
>
> Thanx, Paul
>