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From: Boqun Feng <boqun.feng@gmail.com>
To: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
	rushikesh.s.kadam@intel.com, urezki@gmail.com,
	neeraj.iitr10@gmail.com, frederic@kernel.org, paulmck@kernel.org,
	rostedt@goodmis.org, vineeth@bitbyteword.org
Subject: Re: [PATCH v5 03/18] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask
Date: Tue, 6 Sep 2022 15:26:33 -0700	[thread overview]
Message-ID: <YxfJGYP2l0xbxxdr@boqun-archlinux> (raw)
In-Reply-To: <20220901221720.1105021-4-joel@joelfernandes.org>

On Thu, Sep 01, 2022 at 10:17:05PM +0000, Joel Fernandes (Google) wrote:
> The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This
> may help avoid load/store tearing due to concurrent access, KCSAN

Nit: you can avoid only load tearing with READ_ONCE().

Regards,
Boqun

> issues, and preserve sanity of people reading the mask in tracing.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>  kernel/rcu/tree.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 0ca21ac0f064..5ec97e3f7468 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2106,7 +2106,7 @@ int rcutree_dying_cpu(unsigned int cpu)
>  	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
>  		return 0;
>  
> -	blkd = !!(rnp->qsmask & rdp->grpmask);
> +	blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
>  	trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
>  			       blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
>  	return 0;
> -- 
> 2.37.2.789.g6183377224-goog
> 

  reply	other threads:[~2022-09-06 22:27 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-01 22:17 [PATCH v5 00/18] Implement call_rcu_lazy() and miscellaneous fixes Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 01/18] mm/slub: perform free consistency checks before call_rcu Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 02/18] mm/sl[au]b: rearrange struct slab fields to allow larger rcu_head Joel Fernandes (Google)
2022-09-02  9:26   ` Vlastimil Babka
2022-09-02  9:30     ` Vlastimil Babka
2022-09-02 15:09       ` Joel Fernandes
2022-09-03 13:53         ` Paul E. McKenney
2022-09-01 22:17 ` [PATCH v5 03/18] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask Joel Fernandes (Google)
2022-09-06 22:26   ` Boqun Feng [this message]
2022-09-06 22:31     ` Joel Fernandes
2022-09-01 22:17 ` [PATCH v5 04/18] rcu: Fix late wakeup when flush of bypass cblist happens Joel Fernandes (Google)
2022-09-02 11:35   ` Frederic Weisbecker
2022-09-02 23:58     ` Joel Fernandes
2022-09-03 15:10       ` Paul E. McKenney
2022-09-04 21:13       ` Frederic Weisbecker
2022-09-03 14:04   ` Paul E. McKenney
2022-09-03 14:05     ` Joel Fernandes
2022-09-06  3:07   ` Joel Fernandes
2022-09-06  9:48     ` Frederic Weisbecker
2022-09-07  2:43       ` Joel Fernandes
2022-09-01 22:17 ` [PATCH v5 05/18] rcu: Move trace_rcu_callback() before bypassing Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 06/18] rcu: Introduce call_rcu_lazy() API implementation Joel Fernandes (Google)
2022-09-02 15:21   ` Frederic Weisbecker
2022-09-02 23:09     ` Joel Fernandes
2022-09-05 12:59       ` Frederic Weisbecker
2022-09-05 20:18         ` Joel Fernandes
2022-09-05 20:32         ` Joel Fernandes
2022-09-06  8:55           ` Paul E. McKenney
2022-09-06 16:16             ` Joel Fernandes
2022-09-06 17:05               ` Paul E. McKenney
2022-09-03 22:00     ` Joel Fernandes
2022-09-04 21:01       ` Frederic Weisbecker
2022-09-05 20:20         ` Joel Fernandes
2022-09-06  3:05     ` Joel Fernandes
2022-09-06 15:17       ` Frederic Weisbecker
2022-09-06 16:15         ` Joel Fernandes
2022-09-06 16:31           ` Joel Fernandes
2022-09-06 16:38             ` Joel Fernandes
2022-09-06 16:43               ` Joel Fernandes
2022-09-06 19:11                 ` Frederic Weisbecker
2022-09-07  2:56                   ` Joel Fernandes
2022-09-07  9:56                     ` Frederic Weisbecker
2022-09-07 10:03           ` Frederic Weisbecker
2022-09-07 14:01             ` Joel Fernandes
2022-09-07  0:06         ` Joel Fernandes
2022-09-07  9:40           ` Frederic Weisbecker
2022-09-07 13:44             ` Joel Fernandes
2022-09-07 15:38               ` Frederic Weisbecker
2022-09-07 15:39                 ` Joel Fernandes
2022-09-21 23:52             ` Joel Fernandes
2022-09-06 18:16       ` Uladzislau Rezki
2022-09-06 18:21         ` Joel Fernandes
2022-09-07  8:52           ` Uladzislau Rezki
2022-09-07 15:23             ` Joel Fernandes
2022-09-03 14:03   ` Paul E. McKenney
2022-09-03 14:05     ` Joel Fernandes
2022-09-01 22:17 ` [PATCH v5 07/18] rcu: shrinker for lazy rcu Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 08/18] rcu: Add per-CB tracing for queuing, flush and invocation Joel Fernandes (Google)
2022-09-02 16:48   ` kernel test robot
2022-09-03 12:39     ` Paul E. McKenney
2022-09-03 14:07       ` Joel Fernandes
2022-09-02 19:01   ` kernel test robot
2022-09-01 22:17 ` [PATCH v5 09/18] rcuscale: Add laziness and kfree tests Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 10/18] rcutorture: Add test code for call_rcu_lazy() Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 11/18] fs: Move call_rcu() to call_rcu_lazy() in some paths Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 12/18] cred: Move call_rcu() to call_rcu_lazy() Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 13/18] security: " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 14/18] net/core: " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 15/18] kernel: Move various core kernel usages " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 16/18] lib: Move call_rcu() " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 17/18] i915: " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 18/18] fork: Move thread_stack_free_rcu() " Joel Fernandes (Google)
2022-09-03 15:22 ` [PATCH v5 00/18] Implement call_rcu_lazy() and miscellaneous fixes Paul E. McKenney

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