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Date: Mon, 3 Jun 2019 10:01:28 +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>,
	"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>, rcu@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [RFC 1/6] rcu: Add support for consolidated-RCU reader checking

On Sat, Jun 01, 2019 at 06:27:33PM -0400, Joel Fernandes (Google) wrote:
> +#define list_for_each_entry_rcu(pos, head, member, cond...)		\
> +	if (COUNT_VARGS(cond) != 0) {					\
> +		__list_check_rcu_cond(0, ## cond);			\
> +	} else {							\
> +		__list_check_rcu();					\
> +	}								\
> +	for (pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
> +		&pos->member != (head);					\
>  		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
>  
>  /**
> @@ -621,7 +648,12 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
>   * the _rcu list-mutation primitives such as hlist_add_head_rcu()
>   * as long as the traversal is guarded by rcu_read_lock().
>   */
> +#define hlist_for_each_entry_rcu(pos, head, member, cond...)		\
> +	if (COUNT_VARGS(cond) != 0) {					\
> +		__list_check_rcu_cond(0, ## cond);			\
> +	} else {							\
> +		__list_check_rcu();					\
> +	}								\
>  	for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
>  			typeof(*(pos)), member);			\
>  		pos;							\


This breaks code like:

	if (...)
		list_for_each_entry_rcu(...);

as they are no longer a single statement. You'll have to frob it into
the initializer part of the for statement.

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