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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: rostedt <rostedt@goodmis.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Paul <paulmck@linux.vnet.ibm.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	"Joel Fernandes, Google" <joel@joelfernandes.org>,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	Jozsef Kadlecsik <kadlec@netfilter.org>,
	Florian Westphal <fw@strlen.de>,
	"David S. Miller" <davem@davemloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	David Ahern <dsahern@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>, rcu <rcu@vger.kernel.org>,
	netfilter-devel <netfilter-devel@vger.kernel.org>,
	coreteam@netfilter.org, netdev <netdev@vger.kernel.org>
Subject: Re: [RFC][PATCH] rcu: Use typeof(p) instead of typeof(*p) *
Date: Tue, 5 Oct 2021 11:15:12 -0400 (EDT)	[thread overview]
Message-ID: <505004021.2637.1633446912223.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20211005094728.203ecef2@gandalf.local.home>

----- On Oct 5, 2021, at 9:47 AM, rostedt rostedt@goodmis.org wrote:
[...]
> #define rcu_dereference_raw(p) \
> ({ \
> 	/* Dependency order vs. p above. */ \
> 	typeof(p) ________p1 = READ_ONCE(p); \
> -	((typeof(*p) __force __kernel *)(________p1)); \
> +	((typeof(p) __force __kernel)(________p1)); \
> })

AFAIU doing so removes validation that @p is indeed a pointer, so a user might mistakenly
try to use rcu_dereference() on an integer, and get away with it. I'm not sure we want to
loosen this check. I wonder if there might be another way to achieve the same check without
requiring the structure to be declared, e.g. with __builtin_types_compatible_p ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

  reply	other threads:[~2021-10-05 15:15 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-05 13:47 [RFC][PATCH] rcu: Use typeof(p) instead of typeof(*p) * Steven Rostedt
2021-10-05 15:15 ` Mathieu Desnoyers [this message]
2021-10-05 15:58   ` Steven Rostedt
2021-10-05 16:15     ` Mathieu Desnoyers
2021-10-05 16:29       ` Paul E. McKenney
2021-10-05 16:40       ` Steven Rostedt
2021-10-11  8:39   ` David Laight
2021-10-12 14:18     ` Mathieu Desnoyers
2021-10-12 15:36       ` Steven Rostedt
2021-10-05 16:18 ` Linus Torvalds
2021-10-05 16:37   ` Steven Rostedt
2021-10-05 16:47     ` Linus Torvalds
2021-10-05 16:42   ` Steven Rostedt
2021-10-05 18:01 ` Rasmus Villemoes
2021-10-05 18:06   ` Mathieu Desnoyers
2021-10-05 18:28     ` Jan Engelhardt
2021-10-05 18:40       ` Steven Rostedt
2021-10-05 19:06         ` Jan Engelhardt
2021-10-05 19:40           ` Steven Rostedt
2021-10-05 19:46             ` Linus Torvalds
2021-10-05 20:02               ` Steven Rostedt
2021-10-05 19:49             ` Mathieu Desnoyers
2021-10-05 20:06               ` Steven Rostedt
2021-10-05 20:37             ` Steven Rostedt
2021-10-05 20:45               ` Linus Torvalds
2021-10-05 21:05                 ` Steven Rostedt
2021-10-05 21:09               ` Jan Engelhardt
2021-10-05 21:24                 ` Steven Rostedt
2021-10-11  8:34                   ` David Laight
2021-10-05 21:27                 ` Linus Torvalds
2021-10-05 22:26                   ` Jan Engelhardt
2021-10-05 18:48     ` Rasmus Villemoes

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