On Mon, 2025-02-24 at 15:50 -0500, Mathieu Desnoyers wrote: > On 2025-02-24 08:28, Gabriele Monaco wrote: > [...] > > diff --git a/kernel/rseq.c b/kernel/rseq.c > > index 2cb16091ec0ae..936863fe7eb37 100644 > > --- a/kernel/rseq.c > > +++ b/kernel/rseq.c > > @@ -419,6 +419,7 @@ void __rseq_handle_notify_resume(struct ksignal > > *ksig, struct pt_regs *regs) > > } > > if (unlikely(rseq_update_cpu_node_id(t))) > > goto error; > > + task_queue_mm_cid(t); > > Given that task_queue_mm_cid() will be called quite frequently from > __rseq_handle_notify_resume, perhaps it would be best to move at > least > the portion responsible for checks (including the time_before()) to > include/linux/sched.h to eliminate a function call from the fast > path. > > Right, good idea. Thinking about that, task_queue_mm_cid checks a bit more than the __rseq_handle_notify_resume. As far as I understand, as long as we only call task_queue_mm_cid from __rseq_handle_notify_resume, it won't ever be called from a kthread (I assume the t->rseq implies t->mm and not PF_KTHREAD but also by construction since it's called in return to user). In short, considering we already check for PF_EXITING, the following is just superfluous: if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD))) return; and we could just keep the time_before check in __rseq_handle_notify_resume, perhaps adding a t->mm check just to avoid a perceived NULL pointer dereference, which seems not possible anyway. Am I missing any corner case? Thanks, Gabriele
