On 2026-09-27 12:15, Boqun Feng wrote:
On Sun, Sep 27, 2026 at 11:51:27AM -0400, Mathieu Desnoyers wrote:
Hi Paul,
This series applies on top of "hazptr: handle NULL address in
hazptr_detach" you have in your rcu dev tree.
This first patch addresses a race identified by Boqun Feng in the
two-phase wildcard scheme.
Thank you! That looks good from a quick look. I will give a deep look
later on (I was traveling).
For the following versions/patches, could you also Cc Kuwu Chan and
Liang Wang (Cced) ? They are helping on the scan thread and lockdep
integration, so it'll be good to keep them in the loop. Thank you!
Noted, I've added them to my patch commit messages, so they should
be there for the next round.
Patches 2-3 are prerequisites for using ptr_eq() in the 4th patch.
Those were discussed at length in a prior version of hazard pointer
patches.
Patch 4 introduces a "try acquire" helper to allow the fast path
to not rely on wildcards, while keeping the wildcard forward
progress guarantees in the acquire slow path, used on fast path
failure.
Nice! I want to point out that later on if the reader can handle the
race with the updater (i.e. the readers don't need the progress
guarantees from hazptr, then we can expose a hazptr_try_acquire() for
exactly that). Although I do have some design trade-off questions for
patch 4.
Sure, if you have a use-case in mind I'm interested to hear about it!
Thanks,
Mathieu
Regards,
Boqun
Thanks,
Mathieu
Mathieu Desnoyers (4):
hazptr: Fix two-phase hazptr_synchronize race with detach
compiler.h: Introduce ptr_eq() to preserve address dependency
Documentation: RCU: Refer to ptr_eq()
hazptr: Introduce "try acquire" fast path, fallback to overflow list
Cc: Paul E. McKenney <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Bradley Morgan <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Documentation/RCU/rcu_dereference.rst | 38 +++++++-
include/linux/compiler.h | 63 ++++++++++++
include/linux/hazptr.h | 47 +++++----
kernel/hazptr.c | 135 +++++++++++++++-----------
4 files changed, 203 insertions(+), 80 deletions(-)
--
2.43.0
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
