Re: [PATCH] selftests/rseq: Fix handling of glibc without rseq support

[Shuah Khan <skhan@linuxfoundation.org>]

On 1/14/25 07:51, Mathieu Desnoyers wrote:
> When porting librseq commit:
> 
> commit c7b45750fa85 ("Adapt to glibc __rseq_size feature detection")
> 
> from librseq to the kernel selftests, the following line was missed
> at the end of rseq_init():
> 
>    rseq_size = get_rseq_kernel_feature_size();
> 
> which effectively leaves rseq_size initialized to -1U when glibc does not
> have rseq support. glibc supports rseq from version 2.35 onwards.
> 
> In a following librseq commit
> 
> commit c67d198627c2 ("Only set 'rseq_size' on first thread registration")
> 
> to mimic the libc behavior, a new approach is taken: don't set the
> feature size in 'rseq_size' until at least one thread has successfully
> registered. This allows using 'rseq_size' in fast-paths to test for both
> registration status and available features. The caveat is that on libc
> either all threads are registered or none are, while with bare librseq
> it is the responsability of the user to register all threads using rseq.
> 
> This combines the changes from the following librseq commits:
> 
> commit c7b45750fa85 ("Adapt to glibc __rseq_size feature detection")
> commit c67d198627c2 ("Only set 'rseq_size' on first thread registration")
> 
> Fixes: 73a4f5a704a2 ("selftests/rseq: Fix mm_cid test failure")
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Hi Mathieu,

Can you double check these commits and make sure these are right
ones in the mainline rc7?

I am seeing "Unknown commit id" warnings on all of these - my
repo is at 6.13 rc7

Also would you like to add Reported-by for Raghavendra Rao Ananta?

thanks,
-- Shuah