linux-kernel - Re: [patch 1/2] mm: protect local lock sections with rcu_read

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Message-ID: <5f96c7e306546af4604cfaddb895a089811cb99b.camel@redhat.com>
Date:   Tue, 22 Feb 2022 16:21:26 +0100
From:   Nicolas Saenz Julienne <nsaenzju@...hat.com>
To:     Marcelo Tosatti <mtosatti@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, Minchan Kim <minchan@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Juri Lelli <juril@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [patch 1/2] mm: protect local lock sections with rcu_read_lock
 (on RT)

On Tue, 2022-02-22 at 11:47 -0300, Marcelo Tosatti wrote:
> For the per-CPU LRU page vectors, augment the local lock protected
> code sections with rcu_read_lock.
> 
> This makes it possible to replace the queueing of work items on all 
> CPUs by synchronize_rcu (which is necessary to run FIFO:1 applications
> uninterrupted on isolated CPUs).

I don't think this is needed. In RT local_locks use a spinlock. See
kernel/locking/spinlock_rt.c:

"The RT [spinlock] substitutions explicitly disable migration and take
rcu_read_lock() across the lock held section."

Regards,

-- 
Nicolás Sáenz