On Wed, 6 Jul 2022 21:37:52 +0000
Song Liu <songliubraving@xxxxxx> wrote:
> > Can you comment here that returning -EAGAIN will not cause this to repeat.
> > That it will change things where the next try will not return -EGAIN?
>
> Hmm.. this is not the guarantee here. This conflict is a real race condition
> that an IPMODIFY function (i.e. livepatch) is being registered at the same time
> when something else, for example bpftrace, is updating the BPF trampoline.
>
> This EAGAIN will propagate to the user of the IPMODIFY function (i.e. livepatch),
> and we need to retry there. In the case of livepatch, the retry is initiated
> from user space.
We need to be careful here then. If there's a userspace application that
runs at real-time and does a:
do {
errno = 0;
regsiter_bpf();
} while (errno != -EAGAIN);
it could in theory preempt the owner of the lock and never make any
progress.
-- Steve
