From: Uladzislau Rezki <urezki@gmail.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
LKML <linux-kernel@vger.kernel.org>, RCU <rcu@vger.kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraj.iitr10@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Subject: Re: [PATCH v2 3/4] rcu/kvfree: Move need_offload_krc() out of krcp->lock
Date: Wed, 30 Nov 2022 13:56:17 +0100 [thread overview]
Message-ID: <Y4dS8X+Ir7egYBTD@pc636> (raw)
In-Reply-To: <20221129233833.GA154809@paulmck-ThinkPad-P17-Gen-1>
On Tue, Nov 29, 2022 at 03:38:33PM -0800, Paul E. McKenney wrote:
> On Tue, Nov 29, 2022 at 04:58:21PM +0100, Uladzislau Rezki (Sony) wrote:
> > Currently a need_offload_krc() function requires the krcp->lock
> > to be held because krcp->head can not be checked concurrently.
> >
> > Fix it by updating the krcp->head using WRITE_ONCE() macro so
> > it becomes lock-free and safe for readers to see a valid data
> > without any locking.
>
> Don't we also need to use READ_ONCE() for the code loading this krcp->head
> pointer? Or do the remaining plain C-language accesses somehow avoid
> running concurrently with those new WRITE_ONCE() invocations?
>
It can be concurrent. I was thinking about it. For some reason i decided
to keep readers as a "regular" ones for loading the krcp->head.
In this case it might take time for readers to see an updated value
as a worst case scenario.
So i need to update it or upload one more patch on top of v2. Should
i upload a new patch?
Thanks!
--
Uladzislau Rezki
next prev parent reply other threads:[~2022-11-30 12:56 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-29 15:58 [PATCH v2 0/4] kvfree_rcu() updates related to polled API Uladzislau Rezki (Sony)
2022-11-29 15:58 ` [PATCH v2 1/4] rcu/kvfree: Switch to a generic linked list API Uladzislau Rezki (Sony)
2022-11-29 15:58 ` [PATCH v2 2/4] rcu/kvfree: Move bulk/list reclaim to separate functions Uladzislau Rezki (Sony)
2022-11-29 15:58 ` [PATCH v2 3/4] rcu/kvfree: Move need_offload_krc() out of krcp->lock Uladzislau Rezki (Sony)
2022-11-29 23:38 ` Paul E. McKenney
2022-11-30 12:56 ` Uladzislau Rezki [this message]
2022-11-30 18:44 ` Paul E. McKenney
2022-12-02 13:19 ` Uladzislau Rezki
2022-11-29 15:58 ` [PATCH v2 4/4] rcu/kvfree: Use a polled API to speedup a reclaim process Uladzislau Rezki (Sony)
2022-12-01 23:45 ` Paul E. McKenney
2022-12-02 12:54 ` Uladzislau Rezki
2022-12-02 19:14 ` Paul E. McKenney
2022-11-29 16:37 ` [PATCH v2 0/4] kvfree_rcu() updates related to polled API Paul E. McKenney
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