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Message-ID: <20190712110142.GS3402@hirez.programming.kicks-ass.net>
Date: Fri, 12 Jul 2019 13:01:42 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc: linux-kernel@...r.kernel.org, Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Borislav Petkov <bp@...en8.de>,
	c0d1n61at3@...il.com, "David S. Miller" <davem@...emloft.net>,
	edumazet@...gle.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Josh Triplett <josh@...htriplett.org>, keescook@...omium.org,
	kernel-hardening@...ts.openwall.com,
	Lai Jiangshan <jiangshanlai@...il.com>, Len Brown <lenb@...nel.org>,
	linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-pm@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, neilb@...e.com,
	netdev@...r.kernel.org, oleg@...hat.com,
	"Paul E. McKenney" <paulmck@...ux.ibm.com>,
	Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Rasmus Villemoes <rasmus.villemoes@...vas.dk>, rcu@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>, will@...nel.org,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader
 checking

On Thu, Jul 11, 2019 at 07:43:56PM -0400, Joel Fernandes (Google) wrote:
> This patch adds support for checking RCU reader sections in list
> traversal macros. Optionally, if the list macro is called under SRCU or
> other lock/mutex protection, then appropriate lockdep expressions can be
> passed to make the checks pass.
> 
> Existing list_for_each_entry_rcu() invocations don't need to pass the
> optional fourth argument (cond) unless they are under some non-RCU
> protection and needs to make lockdep check pass.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> ---
>  include/linux/rculist.h  | 29 ++++++++++++++++++++++++-----
>  include/linux/rcupdate.h |  7 +++++++
>  kernel/rcu/Kconfig.debug | 11 +++++++++++
>  kernel/rcu/update.c      | 26 ++++++++++++++++++++++++++
>  4 files changed, 68 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index e91ec9ddcd30..78c15ec6b2c9 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -40,6 +40,23 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
>   */
>  #define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))
>  
> +/*
> + * Check during list traversal that we are within an RCU reader
> + */
> +
> +#define SIXTH_ARG(a1, a2, a3, a4, a5, a6, ...) a6
> +#define COUNT_VARGS(...) SIXTH_ARG(dummy, ## __VA_ARGS__, 4, 3, 2, 1, 0)

You don't seem to actually use it in this patch; also linux/kernel.h has
COUNT_ARGS().

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