Figured out what rcu_read_ongoing does. It just returns true if it's called within a read section and false otherwise. The problem for catching whether reads are done outside read sections is that you can not make macros for read and write operations. e.g. ptr->a = 4;.

tir. 2. sep. 2025 kl. 16:17 skrev Thobias Knudsen <thobknu@gmail.com>:
> I suspect that what you are trying to achieve is validation that
> calls to functions that require to be within a RCU read-side critical
> section such as cds_lfht_lookup are indeed invoked from within a
> critical section.

Yes exactly, but not only for read sections. It could also be to validate that rcu_barrier isnt called within a callback function or that rcu_quiescent_state isnt called when thread is offline

> We've added a "rcu_read_ongoing()" API for that purpose to liburcu
> RCU flavors, but AFAIK it's not used for any kind of validation
> within cds_lfht. This could indeed become a feature request that
> would apply to all liburcu data structure APIs.

I can't find any documentation on rcu_read_ongoing. Btw the documentation for urcu in general is scattered all around the repo it seems. It should have been all at one place imo. Should I make a feature request for it? I don't know how stuff works inside this repo though.



man. 1. sep. 2025 kl. 17:09 skrev Mathieu Desnoyers <mathieu.desnoyers@efficios.com>:
On 2025-08-31 16:48, Thobias Knudsen wrote:
> BTW i've made a macro library which overrides the
> urcu and lfht functions. It checks that you call the functions in the
> correct order. This has been really useful for debugging and I think it
> would be useful to have it integrated into urcu to make the it more user
> friendly. you could have it integrated with the macro DEBUG_RCU or make
> a new one, maybe DEBUG_FUNCTION_CALL_ORDER. The only thing it doesn't
> catch is if you continue to use data from cds_lfht_lookup() after
> rcu_read_unlock()

I suspect that what you are trying to achieve is validation that
calls to functions that require to be within a RCU read-side critical
section such as cds_lfht_lookup are indeed invoked from within a
critical section.

We've added a "rcu_read_ongoing()" API for that purpose to liburcu
RCU flavors, but AFAIK it's not used for any kind of validation
within cds_lfht. This could indeed become a feature request that
would apply to all liburcu data structure APIs.

Thanks,

Mathieu

>
> søn. 31. aug. 2025 kl. 22:42 skrev Thobias Knudsen <thobknu@gmail.com
> <mailto:thobknu@gmail.com>>:
>
>     First question: why isn't Userspace RCU more popular?
>     Second question: Why isn't it possible to create issues in the urcu
>     repo? Im asking for a feature here:
>     Is it possible to make a function which checks if there are more
>     callbacks queued by call_rcu? I need that because there are some
>     callbacks which call call_rcu, and then calling rcu_barrier once
>     isn't enough and I therefore need a way to check if there are still
>     callbacks to wait on before terminating the program. No worries if
>     this is too much to ask for or if it isn't possible. This
>     functionality is only needed in termination because otherwise
>     isn't needed to call rcu_barrier multiple times (at least so far)
>
>     Best regards
>     Thobias
>
>


--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com