From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
eric.dumazet@gmail.com
Subject: Re: [PATCH tip/core/rcu 5/8] rcu: only one evaluation of arg in rcu_dereference_check() unless sparse
Date: Thu, 23 Sep 2010 10:23:37 -0700 [thread overview]
Message-ID: <20100923172337.GF2406@linux.vnet.ibm.com> (raw)
In-Reply-To: <201009231513.40126.arnd@arndb.de>
On Thu, Sep 23, 2010 at 03:13:39PM +0200, Arnd Bergmann wrote:
> On Thursday 23 September 2010, Paul E. McKenney wrote:
> > The current version of the __rcu_access_pointer(), __rcu_dereference_check(),
> > and __rcu_dereference_protected() macros evaluate their "p" argument
> > three times, not counting typeof()s. This is bad news if that argument
> > contains a side effect. This commit therefore evaluates this argument
> > only once in normal kernel builds. However, the straightforward approach
> > defeats sparse's RCU-pointer checking, so when __CHECKER__ is defined,
> > the additional pair of evaluations of the "p" argument are performed in
> > order to permit sparse to detect misuse of RCU-protected pointers.
> >
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
>
> Sorry for not following up with the alternative approach yet. We can always
> do that later, for your patch should go into 2.6.36 to fix any problems
> arising from unintended macro side-effects.
>
> Acked-by: Arnd Bergmann <arnd@arndb.de>
No problem, when you get me a better approach, I will happily queue it!
Thanx, Paul
next prev parent reply other threads:[~2010-09-23 17:23 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-23 0:50 [PATCH tip/core/rcu 0/8] random RCU fixes and updates Paul E. McKenney
2010-09-23 0:50 ` [PATCH tip/core/rcu 1/8] rcu: upgrade stallwarn.txt documentation for CPU-bound RT processes Paul E. McKenney
2010-09-23 0:50 ` [PATCH tip/core/rcu 2/8] rcu: performance fixes to TINY_PREEMPT_RCU callback checking Paul E. McKenney
2010-09-23 0:50 ` [PATCH tip/core/rcu 3/8] rcu: fix _oddness handling of verbose stall warnings Paul E. McKenney
2010-09-23 0:50 ` [PATCH tip/core/rcu 4/8] kernel: Removing undead ifdef CONFIG_DEBUG_LOCK_ALLOC Paul E. McKenney
2010-09-23 0:50 ` [PATCH tip/core/rcu 5/8] rcu: only one evaluation of arg in rcu_dereference_check() unless sparse Paul E. McKenney
2010-09-23 13:13 ` Arnd Bergmann
2010-09-23 17:23 ` Paul E. McKenney [this message]
2010-09-23 0:50 ` [PATCH tip/core/rcu 6/8] rcu: fix sparse errors in rcutorture.c Paul E. McKenney
2010-09-23 0:50 ` [PATCH tip/core/rcu 7/8] rcu: Add tracing data to support queueing models Paul E. McKenney
2010-09-23 0:50 ` [PATCH tip/core/rcu 8/8] rcu: Add advice to PROVE_RCU_REPEATEDLY kernel config parameter Paul E. McKenney
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