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

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Message-ID: <75830847-a2ab-4bf4-bd4c-f7695e48ea3d@paulmck-laptop>
Date: Tue, 16 Jan 2024 11:10:14 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
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 Tue, Jan 16, 2024 at 07:10:59PM +0100, Oleg Nesterov wrote:
> 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>

Queued, thank you all!

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

I am clearly not keeping up.  ;-)

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

Good to know!  I added this to the commit log, so please let me know
if this is in any way inappropriate:

------------------------------------------------------------------------

In the words of Oleg Nesterov:

	__rcu_sync_enter(wait => false) is a better alternative if
	someone needs rcu_sync_enter_start() again.

Link: https://lore.kernel.org/all/20220725121208.GB28662@redhat.com/

------------------------------------------------------------------------

> 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.

Thank you for the background information, much appreciated!

							Thanx, Paul