linux-kernel - Re: [PATCH 1/1] rcu/tree: Drop the lock before entering to page allocator

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Message-ID: <20200715185628.7b4k3o5efp4gnbla@linutronix.de>
Date:   Wed, 15 Jul 2020 20:56:28 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        linux-mm@...ck.org, "Paul E . McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH 1/1] rcu/tree: Drop the lock before entering to page
 allocator

On 2020-07-15 20:35:37 [+0200], Uladzislau Rezki (Sony) wrote:
> @@ -3306,6 +3307,9 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr)
>  			if (IS_ENABLED(CONFIG_PREEMPT_RT))
>  				return false;
>  
> +			preempt_disable();
> +			krc_this_cpu_unlock(*krcp, *flags);

Now you enter memory allocator with disabled preemption. This isn't any
better but we don't have a warning for this yet.
What happened to the part where I asked for a spinlock_t?

> +
>  			/*
>  			 * NOTE: For one argument of kvfree_rcu() we can
>  			 * drop the lock and get the page in sleepable

Sebastian