linux-kernel - Re: [PATCH v7 0/4] lockinig/rwsem: Fix rwsem bugs & enable true lock handoff

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Date:   Thu, 26 Jan 2023 13:46:22 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        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 v7 0/4] lockinig/rwsem: Fix rwsem bugs & enable true lock
 handoff


* Waiman Long <longman@...hat.com> wrote:

> v7:
>  - Add a comment to down_read_non_owner() in patch 2.
>  - Drop v6 patches 4 & 6 and simplify the direct rwsem lock handoff
>    patch as suggested by PeterZ.
> 
> 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.
> 
> 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 (4):
>   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: Enable direct rwsem lock handoff
> 
>  kernel/locking/rwsem.c | 161 +++++++++++++++++++++++++++++------------
>  1 file changed, 115 insertions(+), 46 deletions(-)

So as a first step I've applied the first 3 patches to the locking tree, 
which are arguably fixes.

Thanks,

	Ingo