On 2023-10-30 14:19, Steven Rostedt wrote:
On Mon, 30 Oct 2023 14:05:05 -0400
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
If you have the nesting counter, why do you need the explicit on/off
switch ?
Because I gave up when I found that one of the lwlocks seemed to take a long
time (pretty much the entire test) or I couldn't find how it was unlocked
(the code isn't trivial).
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.
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.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
