linux-kernel - Re: [PATCH 1/1] rcu/sync: remove un-used rcu_sync_enter

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Message-ID: <20240116181058.GB12342@redhat.com>
Date: Tue, 16 Jan 2024 19:10:59 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Onkarnarth <onkarnath.1@...sung.com>, frederic@...nel.org,
	quic_neeraju@...cinc.com, joel@...lfernandes.org,
	josh@...htriplett.org, boqun.feng@...il.com, rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
	qiang.zhang1211@...il.com, rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org, r.thapliyal@...sung.com,
	maninder1.s@...sung.com, tj@...nel.org, peterz@...radead.org
Subject: Re: [PATCH 1/1] rcu/sync: remove un-used rcu_sync_enter_start
 function

On 01/16, Paul E. McKenney wrote:
>
> On Thu, Jan 11, 2024 at 02:57:22PM +0530, Onkarnarth wrote:
> > From: Onkarnath <onkarnath.1@...sung.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@...sung.com>
> > Signed-off-by: Maninder Singh <maninder1.s@...sung.com>

Acked-by: Oleg Nesterov <oleg@...hat.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.