Commit 14cd5d4a authored by Mark Rutland's avatar Mark Rutland Committed by Ingo Molnar
Browse files

locking/atomics, net/netlink/netfilter: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE() 



For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't currently harmful.

However, for some features it is necessary to instrument reads and
writes separately, which is not possible with ACCESS_ONCE(). This
distinction is critical to correct operation.

It's possible to transform the bulk of kernel code using the Coccinelle
script below. However, this doesn't handle comments, leaving references
to ACCESS_ONCE() instances which have been removed. As a preparatory
step, this patch converts netlink and netfilter code and comments to use
{READ,WRITE}_ONCE() consistently.

----
virtual patch

@ depends on patch @
expression E1, E2;
@@

- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)

@ depends on patch @
expression E;
@@

- ACCESS_ONCE(E)
+ READ_ONCE(E)
----

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Florian Westphal <fw@strlen.de>
Cc: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-7-git-send-email-paulmck@linux.vnet.ibm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 24fbd6e0

include/linux/genetlink.h

+1 −1
Original line number Diff line number Diff line
@@ -30,7 +30,7 @@ extern wait_queue_head_t genl_sk_destructing_waitq; 
 * @p: The pointer to read, prior to dereferencing

 *

 * Return the value of the specified RCU-protected pointer, but omit

 * both the smp_read_barrier_depends() and the ACCESS_ONCE(), because

 * both the smp_read_barrier_depends() and the READ_ONCE(), because

 * caller holds genl mutex.

 */

#define genl_dereference(p)					\

include/linux/netfilter/nfnetlink.h

+1 −1
Original line number Diff line number Diff line
@@ -66,7 +66,7 @@ static inline bool lockdep_nfnl_is_held(__u8 subsys_id) 
 * @ss: The nfnetlink subsystem ID

 *

 * Return the value of the specified RCU-protected pointer, but omit

 * both the smp_read_barrier_depends() and the ACCESS_ONCE(), because

 * both the smp_read_barrier_depends() and the READ_ONCE(), because

 * caller holds the NFNL subsystem mutex.

 */

#define nfnl_dereference(p, ss)					\

include/linux/rtnetlink.h

+1 −1
Original line number Diff line number Diff line
@@ -67,7 +67,7 @@ static inline bool lockdep_rtnl_is_held(void) 
 * @p: The pointer to read, prior to dereferencing

 *

 * Return the value of the specified RCU-protected pointer, but omit

 * both the smp_read_barrier_depends() and the ACCESS_ONCE(), because

 * both the smp_read_barrier_depends() and the READ_ONCE(), because

 * caller holds RTNL.

 */

#define rtnl_dereference(p)					\

include/net/netfilter/nf_tables.h

+2 −2
Original line number Diff line number Diff line
@@ -1164,8 +1164,8 @@ static inline u8 nft_genmask_next(const struct net *net) 


static inline u8 nft_genmask_cur(const struct net *net)

{

	/* Use ACCESS_ONCE() to prevent refetching the value for atomicity */

	return 1 << ACCESS_ONCE(net->nft.gencursor);

	/* Use READ_ONCE() to prevent refetching the value for atomicity */

	return 1 << READ_ONCE(net->nft.gencursor);

}



#define NFT_GENMASK_ANY		((1 << 0) | (1 << 1))

net/netfilter/ipvs/ip_vs_sync.c

+1 −1
Original line number Diff line number Diff line
@@ -457,7 +457,7 @@ static inline bool in_persistence(struct ip_vs_conn *cp) 
static int ip_vs_sync_conn_needed(struct netns_ipvs *ipvs,

				  struct ip_vs_conn *cp, int pkts)

{

	unsigned long orig = ACCESS_ONCE(cp->sync_endtime);

	unsigned long orig = READ_ONCE(cp->sync_endtime);

	unsigned long now = jiffies;

	unsigned long n = (now + cp->timeout) & ~3UL;

	unsigned int sync_refresh_period;

CRA Git | Maintained and supported by SUSTech CRA and CCSE