On Fri, Aug 21, 2026 at 12:53:22PM +0100, David Woodhouse wrote:
> On Fri, 2026-08-21 at 11:22 +0800, Kunwu Chan wrote:
[ . . . ]
> > When applying this to current rcu/dev, the patch also needs to account
> > for the additional bool is_atomic argument to
> > check_init_srcu_struct(). Please rebase accordingly.
>
> Ooh, shiny, I hadn't spotted that the atomic thing had landed. Maybe I
> should retract my 'if we get that' above... but let's see how it
> survives.
It is starting to shape up. Here is what is left, that I know of, anyway:
o A bit more work to get rcutorture to put up with atomic SRCU.
o Tree synchronize_srcu_atomic() fastpath.
o Disable preemption.
o Reorganize commits to fix the Tiny hunks that got applied
in Tree commits, and likely other similar issues.
o More work on error checking for use of banned primitives
with atomic SRCU.
o Update documentation.
Not that it matters, but atomic Tiny SRCU seems to be doing quite well.
> I also have more than just this patch to rebase onto rcu/dev — unlike
> some, I'm not just hacking RCU for the fun of it; I get my jollies
> elsewhere :)
>
> Btw, the current commit c68271c3f83a message says "no index flip, no
> grace-period sequence update" but that isn't true of the implementation
> any more, is it? In fact, it *always* does those things, and doesn't
> take the try-path optimisation by counting both epochs, that I'm doing
> here?
The current "dev" branch is here:
dc5bf5c8fb26 ("fixup! srcutree: Add an atomic Tree SRCU").
Tree SRCU always does an index flip, though a single index flip can
serve multiple concurrent calls to synchronze_srcu_atomic().
Tiny SRCU has the fast path, but must advance the index anyway for the
benefit of get_state_synchronize_srcu() and friends. It just bumps it
in one shot.
Tree SRCU will also have to bump the index, but will be able to
do so manually, without doing all the grace-period processing.
> Thanks for the careful review.
What David said! ;-)
Thanx, Paul
