Re: [PATCH hazptr 0/4] Hazard pointer updates

[Bradley Morgan]

On 27 September 2026 17:20:36 BST, Mathieu Desnoyers
<mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>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.
>

Maybe my tests could help you? Sorry to impede but the things I sent may
need a but if discussi9n around it

>> 
>>> 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 <paulmck@xxxxxxxxxx>
>>> Cc: Boqun Feng <boqun@xxxxxxxxxx>
>>> Cc: Bradley Morgan <brads@xxxxxxxxxxxxxx>
>>> Cc: Gary Guo <gary@xxxxxxxxxxx>
>>> Cc: <rcu@xxxxxxxxxxxxxxx>
>>> Cc: <lkmm@xxxxxxxxxxxxxxx>
>>> 
>>>   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
>>> 
>
>
>

--- Thanks!
https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@xxxxxxxxx/