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Date:   Tue, 3 Jan 2023 13:13:53 +0100
From:   Frederic Weisbecker <frederic@kernel.org>
To:     "Zhang, Qiang1" <qiang1.zhang@intel.com>
Cc:     "paulmck@kernel.org" <paulmck@kernel.org>,
        "quic_neeraju@quicinc.com" <quic_neeraju@quicinc.com>,
        "joel@joelfernandes.org" <joel@joelfernandes.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] rcu: Fix race in set and clear TICK_DEP_BIT_RCU_EXP
 bitmask
Message-ID: <Y7QcAe+l2J3NtRB6@lothringen>
References: <20221220112520.3596920-1-qiang1.zhang@intel.com>
 <20221221200849.GG4001@paulmck-ThinkPad-P17-Gen-1>
 <20221231182508.GB205110@lothringen>
 <20221231190107.GX4001@paulmck-ThinkPad-P17-Gen-1>
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On Sun, Jan 01, 2023 at 09:41:57AM +0000, Zhang, Qiang1 wrote:
> > > >On Sat, Dec 31, 2022 at 07:25:08PM +0100, Frederic Weisbecker wrote:
> 
> Yes,    and I have a question,  we forcing the tick dependency because the expedited grace period
> is not end for the first time, this means that it is not to set the tick dependency every time.
> if we set the tick dependency in rcu_exp_handler(), does this mean that every time the expedited
> grace period starts the tick dependency will be set unconditionally ?
> 
> Thoughts ?

Only if rcu_exp_handler() fails to report a quiescent state. Then it means we
must poll on the CPU looking for a future one.

In fact the tick dependency should be set when rdp->cpu_no_qs.b.exp is set to
true and cleared when rdp->cpu_no_qs.b.exp is set to false.

Thanks.

> 
> Thanks
> Zqiang
> 
> >
> >							Thanx, Paul