linux-kernel - Re: [PATCH v6 0/6] lockinig/rwsem: Fix rwsem bugs & enable true lock handoff

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Date:   Tue, 17 Jan 2023 15:53:22 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     linux-kernel@...r.kernel.org, john.p.donnelly@...cle.com,
        Hillf Danton <hdanton@...a.com>,
        Mukesh Ojha <quic_mojha@...cinc.com>,
        Ting11 Wang 王婷 <wangting11@...omi.com>
Subject: Re: [PATCH v6 0/6] lockinig/rwsem: Fix rwsem bugs & enable true lock
 handoff

On 11/17/22 21:20, Waiman Long wrote:
> v6:
>   - Fix an error in patch 2 reported by kernel test robot.
>
> v5:
>   - Drop patch 2 and replace it with 2 new patches disabling preemption on
>     all reader functions and writer functions respectively. The other
>     patches are adjusted accordingly.
>
> v4:
>   - Update patch descriptions in patches 1 & 2 to make clear the live
>     lock conditions that are being fixed by these patches. There is no code
>     change from v3.
>
> It turns out the current waiter optimistic spinning code does not work
> that well if we have RT tasks in the mix. This patch series include two
> different fixes to resolve those issues. The last 3 patches modify the
> handoff code to implement true lock handoff similar to that of mutex.
>
> Waiman Long (6):
>    locking/rwsem: Prevent non-first waiter from spinning in down_write()
>      slowpath
>    locking/rwsem: Disable preemption at all down_read*() and up_read()
>      code paths
>    locking/rwsem: Disable preemption at all down_write*() and up_write()
>      code paths
>    locking/rwsem: Change waiter->hanodff_set to a handoff_state enum
>    locking/rwsem: Enable direct rwsem lock handoff
>    locking/rwsem: Update handoff lock events tracking
>
>   kernel/locking/lock_events_list.h |   6 +-
>   kernel/locking/rwsem.c            | 240 ++++++++++++++++++++++--------
>   2 files changed, 182 insertions(+), 64 deletions(-)
>
Peter,

I know that you are busy these days. Do have any further comment or 
suggestion on this patch series?

Looking forward to your reply.

Thanks,
Longman