On Mon, 30 Oct 2023 14:27:10 -0400 Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > > So I just made every unlock disable the extended time slot. I need to go > > back and enable both a counter and an on/off as I now realize that the spin > > locks (called within the lwlock) will disable the extend time before the > > lwlock is released. This should work if I have the spinlocks inc and dec > > (they are straight forward and all locks are associated with an easily > > found unlock), and have the lwlock use bit 31 as an on/off switch. > > This extra on/off switch appears to be working around userspace issues. Yep! But that doesn't mean there's not a legitimate use case for it. I don't want to limit the feature for that. It's unlikely bit 31 would ever be hit by a counter anyway, for which it could be used as an on/off switch the same way the NEED_RESCHED bit is used as an on/off switch for preempt_count in the kernel. > > > Anyway, I would let user space decide what it wants to do, and giving it 31 > > bits to say "I'm extended" and let user space come up with how it handles > > those 31 bits. > > If this makes it into the RSEQ uapi, RSEQ should state how userspace > should collaborate wrt those bits (e.g. nesting counter protocol), even > though it's not a kernel ABI per se. Otherwise we'll just push this to > libc to specify this, which is odd. I agree that user space should have the usage specified. Hell, that bit could just be used for testing purposes. I think having it reserved is a good thing than not specifying it and limiting its usage later. -- Steve
