linux-kernel - Re: [PATCH 4.4 1/3] futex: Change locking rules

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Date:   Tue, 9 Mar 2021 11:40:16 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Yejian <zhengyejian1@...wei.com>
Cc:     lee.jones@...aro.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        cj.chengjian@...wei.com, judy.chenhui@...wei.com,
        zhangjinhao2@...wei.com, nixiaoming@...wei.com
Subject: Re: [PATCH 4.4 1/3] futex: Change locking rules

On Tue, Mar 09, 2021 at 11:06:03AM +0800, Zheng Yejian wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> Currently futex-pi relies on hb->lock to serialize everything. But hb->lock
> creates another set of problems, especially priority inversions on RT where
> hb->lock becomes a rt_mutex itself.
> 
> The rt_mutex::wait_lock is the most obvious protection for keeping the
> futex user space value and the kernel internal pi_state in sync.
> 
> Rework and document the locking so rt_mutex::wait_lock is held accross all
> operations which modify the user space value and the pi state.
> 
> This allows to invoke rt_mutex_unlock() (including deboost) without holding
> hb->lock as a next step.
> 
> Nothing yet relies on the new locking rules.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: juri.lelli@....com
> Cc: bigeasy@...utronix.de
> Cc: xlpang@...hat.com
> Cc: rostedt@...dmis.org
> Cc: mathieu.desnoyers@...icios.com
> Cc: jdesfossez@...icios.com
> Cc: dvhart@...radead.org
> Cc: bristot@...hat.com
> Link: http://lkml.kernel.org/r/20170322104151.751993333@infradead.org
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> [Lee: Back-ported in support of a previous futex back-port attempt]
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> ---
>  kernel/futex.c | 138 +++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 112 insertions(+), 26 deletions(-)

What is the git commit id of this patch in Linus's tree?

thanks,

greg k-h