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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
	peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com,
	edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com,
	sbw@mit.edu, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 13/14] rcu: Make rcu_assign_pointer's assignment volatile and type-safe
Date: Fri, 15 Nov 2013 16:40:16 -0800	[thread overview]
Message-ID: <1384562417-817-13-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com>

From: Josh Triplett <josh@joshtriplett.org>

rcu_assign_pointer needs to use ACCESS_ONCE to make the assignment to
the destination pointer volatile, to protect against compilers too
clever for their own good.

In addition, since rcu_assign_pointer force-casts the source pointer to
add the __rcu address space (overriding any existing address space), add
an explicit check that the source pointer has the __kernel address space
to start with.

This new check produces warnings like this, when attempting to assign
from a __user pointer:

test.c:25:9: warning: incorrect type in argument 2 (different address spaces)
test.c:25:9:    expected struct foo *<noident>
test.c:25:9:    got struct foo [noderef] <asn:1>*badsrc

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 00ad28168ef0..08c961fa7699 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -506,8 +506,17 @@ static inline void rcu_preempt_sleep_check(void)
 #ifdef __CHECKER__
 #define rcu_dereference_sparse(p, space) \
 	((void)(((typeof(*p) space *)p) == p))
+/* The dummy first argument in __rcu_assign_pointer_typecheck makes the
+ * typechecked pointer the second argument, matching rcu_assign_pointer itself;
+ * this avoids confusion about argument numbers in warning messages. */
+#define __rcu_assign_pointer_check_kernel(v) \
+	do { \
+		extern void __rcu_assign_pointer_typecheck(int, typeof(*(v)) __kernel *); \
+		__rcu_assign_pointer_typecheck(0, v); \
+	} while (0)
 #else /* #ifdef __CHECKER__ */
 #define rcu_dereference_sparse(p, space)
+#define __rcu_assign_pointer_check_kernel(v) do { } while (0)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __rcu_access_pointer(p, space) \
@@ -551,7 +560,8 @@ static inline void rcu_preempt_sleep_check(void)
 #define __rcu_assign_pointer(p, v, space) \
 	do { \
 		smp_wmb(); \
-		(p) = (typeof(*v) __force space *)(v); \
+		__rcu_assign_pointer_check_kernel(v); \
+		ACCESS_ONCE(p) = (typeof(*(v)) __force space *)(v); \
 	} while (0)
 
 
-- 
1.8.1.5


  parent reply	other threads:[~2013-11-16  0:45 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-11-16  0:39 [PATCH tip/core/rcu 0/14] sparse improvements of rcu_assign_pointer() for 3.14 Paul E. McKenney
2013-11-16  0:40 ` [PATCH tip/core/rcu 01/14] rcu: Add comment on evaluate-once properties of rcu_assign_pointer() Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 02/14] notifiers: Apply ACCESS_ONCE() to avoid sparse false positive Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 03/14] bridge: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 04/14] decnet: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 05/14] ipv4/ip_socketglue: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 06/14] ipv6/ip6_tunnel: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 07/14] ipv6/ip6_gre: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 08/14] ipv6/sit: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 09/14] mac80211: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 10/14] bridge/br_mdb: " Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 11/14] bonding/bond_main: " Paul E. McKenney
2013-11-16  4:32     ` Ding Tianhong
2013-11-16 15:21       ` Paul E. McKenney
2013-11-16  0:40   ` [PATCH tip/core/rcu 12/14] bonding/bond_alb.c: " Paul E. McKenney
2013-11-16  0:40   ` Paul E. McKenney [this message]
2013-11-16  0:40   ` [PATCH tip/core/rcu 14/14] rcu: Add an RCU_INITIALIZER for global RCU-protected pointers Paul E. McKenney

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