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Date: Tue, 16 Jan 2024 19:10:59 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Onkarnarth <onkarnath.1@samsung.com>, frederic@kernel.org,
	quic_neeraju@quicinc.com, joel@joelfernandes.org,
	josh@joshtriplett.org, boqun.feng@gmail.com, rostedt@goodmis.org,
	mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
	qiang.zhang1211@gmail.com, rcu@vger.kernel.org,
	linux-kernel@vger.kernel.org, r.thapliyal@samsung.com,
	maninder1.s@samsung.com, tj@kernel.org, peterz@infradead.org
Subject: Re: [PATCH 1/1] rcu/sync: remove un-used rcu_sync_enter_start
 function
Message-ID: <20240116181058.GB12342@redhat.com>
References: <CGME20240111092805epcas5p2ebb993010ae31d039e8f9de1e7818f7c@epcas5p2.samsung.com>
 <20240111092722.322454-1-onkarnath.1@samsung.com>
 <de792eee-1f44-48e2-a122-c3ded1645155@paulmck-laptop>
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On 01/16, Paul E. McKenney wrote:
>
> On Thu, Jan 11, 2024 at 02:57:22PM +0530, Onkarnarth wrote:
> > From: Onkarnath <onkarnath.1@samsung.com>
> >
> > With commit '6a010a49b63a ("cgroup: Make !percpu threadgroup_rwsem
> > operations optional")' usage of rcu_sync_enter_start is removed.
> >
> > So this function can also be removed.
> >
> > Signed-off-by: Onkarnath <onkarnath.1@samsung.com>
> > Signed-off-by: Maninder Singh <maninder1.s@samsung.com>

Acked-by: Oleg Nesterov <oleg@redhat.com>


For the record, this was already discussed, see
https://lore.kernel.org/all/20220725121208.GB28662@redhat.com/

Note also the patch in this message, __rcu_sync_enter(wait => false)
is a better alternative if someone needs rcu_sync_enter_start() again.

This patch probably makes sense anyway. Not only cgroup_favor_dynmods()
can use __rcu_sync_enter(), freeze_super() can use it too to avoid
3 synchronize_rcu()'s in a row.

Oleg.