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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Greg KH <gregkh@linuxfoundation.org>, stable@vger.kernel.org,
        Mel Gorman <mgorman@techsingularity.net>,
        Jan Kara <jack@suse.cz>
Subject: Re: [PATCH] rtmutex: Add acquire semantics for rtmutex lock
 acquisition slow path
In-Reply-To: <20230421160947.Sh0eyEWC@linutronix.de>
References: <20230418154315.9PD52J2N@linutronix.de>
 <2023041854-cranium-prone-b9fa@gregkh>
 <20230419072546.gD_YO2-K@linutronix.de> <87pm7x3d8b.ffs@tglx>
 <ZEKFWx_68PX3pk3g@kroah.com> <87ildp2qy7.ffs@tglx>
 <20230421160947.Sh0eyEWC@linutronix.de>
Date:   Fri, 21 Apr 2023 18:33:30 +0200
Message-ID: <87edod2o11.ffs@tglx>
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On Fri, Apr 21 2023 at 18:09, Sebastian Andrzej Siewior wrote:
> On 2023-04-21 17:30:24 [+0200], Thomas Gleixner wrote:
>> >> > The out-of-tree RT patches make extensive use of the code. Since it is
>> >> > upstream code, I assumed it should go via the official stable trees.
>> >> > Without RT, the code is limited the rt_mutex_lock() used by I2C and the
>> >> > RCU booster-mutex.
>> >> 
>> >> Which is a reason to route it through the upstream stable trees, no?
>> >
>> > I do not understand.  Why would we take a patch in the stable tree
>> > because an out-of-tree change requires it?
>> 
>> The change is to the rtmutex core which _IS_ used in tree by futex, RCU
>> and some drivers.
>
> not back stab but to clarify: futex does not use the annotation (it does
> not use the fastpath) but RCU-boosting _and_ I2C-bus code does use it.

Futex requires it too, really. The patch is about the slowpath, no?