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From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
	jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
	dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com,
	fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com
Subject: Re: [PATCH tip/core/rcu 07/12] rcu: No ordering for rcu_assign_pointer() of NULL
Date: Thu, 16 Jun 2016 00:03:39 +0200	[thread overview]
Message-ID: <20160615220339.GZ30921@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1466027173-5501-7-git-send-email-paulmck@linux.vnet.ibm.com>

On Wed, Jun 15, 2016 at 02:46:08PM -0700, Paul E. McKenney wrote:
> This commit does a compile-time check for rcu_assign_pointer() of NULL,
> and uses WRITE_ONCE() rather than smp_store_release() in that case.
> 
> Reported-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
>  include/linux/rcupdate.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index c61b6b9506e7..9be61e47badc 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -650,7 +650,16 @@ static inline void rcu_preempt_sleep_check(void)
>   * please be careful when making changes to rcu_assign_pointer() and the
>   * other macros that it invokes.
>   */
> -#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
> +#define rcu_assign_pointer(p, v) \
> +({ \
> +	uintptr_t _r_a_p__v = (uintptr_t)(v); \
> +	\
> +	if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
> +		WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
> +	else \
> +		smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
> +	_r_a_p__v; \
> +})

Can we pretty please right align the '\'s ?

Also, didn't we used to do this and then reverted it again for some
obscure reason?

  reply	other threads:[~2016-06-15 22:03 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-15 21:45 [PATCH tip/core/rcu 0/12] Miscellaneous RCU fixes for 4.8 Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 01/12] rcu: Fix outdated rcu_scheduler_active comment Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 02/12] rcu: Fix outdated hotplug-exclusion comment in rcu_gp_init() Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 03/12] rcu: Remove some superfluous lines Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 04/12] rcu: Move expedited code from tree.c to tree_exp.h Paul E. McKenney
2016-06-15 22:05   ` Peter Zijlstra
2016-06-15 22:16     ` Paul E. McKenney
2016-06-17 15:48   ` Pranith Kumar
2016-06-17 17:46     ` Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 05/12] rcu: Move expedited code from tree_plugin.h " Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 06/12] rcu: Document RCU_NONIDLE() restrictions in comment header Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 07/12] rcu: No ordering for rcu_assign_pointer() of NULL Paul E. McKenney
2016-06-15 22:03   ` Peter Zijlstra [this message]
2016-06-15 22:12     ` Peter Zijlstra
2016-06-15 22:41       ` Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 08/12] rcu: Disable TASKS_RCU for usermode Linux Paul E. McKenney
2016-06-15 21:47   ` Richard Weinberger
2016-06-15 21:46 ` [PATCH tip/core/rcu 09/12] rcu: Make call_rcu_tasks() tolerate first call with irqs disabled Paul E. McKenney
2016-06-15 22:15   ` Peter Zijlstra
2016-06-15 22:54     ` Paul E. McKenney
2016-06-15 22:16   ` Peter Zijlstra
2016-06-15 22:58     ` Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 10/12] rcu: Fix a typo in a comment Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 11/12] rcu: sysctl: Panic on RCU Stall Paul E. McKenney
2016-06-15 21:46 ` [PATCH tip/core/rcu 12/12] rcu: Correctly handle sparse possible cpus Paul E. McKenney

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