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From:   Yun Levi <ppbuk5246@gmail.com>
Date:   Mon, 24 Jul 2023 09:59:54 +0100
Message-ID: <CAM7-yPSA8E-35w3O=1FLf+=9ax+E1T+eTAfwCscAgzWN2T4Htg@mail.gmail.com>
Subject: Re: [PATCH] rcu: remove unnecessary check cpu_no_qs.norm on rcu_report_qs_rdp
To:     Z qiang <qiang.zhang1211@gmail.com>
Cc:     paulmck@kernel.org, frederic@kernel.org, quic_neeraju@quicinc.com,
        joel@joelfernandes.org, boqun.feng@gmail.com, rostedt@goodmis.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        rcu@vger.kernel.org, linux-kernel@vger.kernel.org
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Hi, Z qiang.

> Maybe this "start new gp"  note misunderstood you.
> For built with CONFIG_RCU_STRICT_GRACE_PERIOD=3Dy and CONFIG_PREEMPT=3Dn =
kernels=EF=BC=8C
> if the gp kthread start a new GP before we exit the RCU read critical sec=
tion,
> and just before we call rcu_report_qs_rdp() in
> rcu_read_unlock_strict(), at this time if the clock irq
> happens and find that the "rcu_seq_current(&rnp->gp_seq) !=3D
> rdp->gp_seq" is true in rcu_pening(),
> will trigger RCU softirq and find that the rcu_seq_new_gp(rdp->gp_seq,
> rnp->gp_seq) is true,
> will  set rdp->cpu_no_qs.b.norm is true. when we return from the
> softirq and call rcu_report_qs_rdp()
> in rcu_read_unlock_strict(), find that the rdp->cpu_no_qs.b.norm is true.
> so there is a situation where the rdp->cpu_no_qs.b.norm is true.

Thanks for making me out from my misunderstanding..!
and even the not in STRICT_GRACE_PERIOD,
old grace period's qs could be reported though rcu_gp_kthread start new gp
by first rcu_report_qs_rdp, will be clear soon by continuous rcu_report_qs_=
rdp
which is triggered by interrupting before the first rcu_report_qs_rdp.

Many thanks..!

And sorry to make noise...!