From 24fbd6e04e4e4793ec9dd9c2e007b0b38d2ec3ab Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 23 Oct 2017 14:07:16 -0700 Subject: [PATCH] locking/atomics, media/dvb_ringbuffer: 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 the DVB ringbuffer 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: Mark Rutland Signed-off-by: Paul E. McKenney Cc: Linus Torvalds Cc: Mauro Carvalho Chehab Cc: Peter Zijlstra Cc: Sakari Ailus Cc: Thomas Gleixner Cc: davem@davemloft.net 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/1508792849-3115-6-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- drivers/media/dvb-core/dvb_ringbuffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c b/drivers/media/dvb-core/dvb_ringbuffer.c index 2322af1b8742..53011629c9ad 100644 --- a/drivers/media/dvb-core/dvb_ringbuffer.c +++ b/drivers/media/dvb-core/dvb_ringbuffer.c @@ -66,12 +66,12 @@ ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf) { ssize_t free; - /* ACCESS_ONCE() to load read pointer on writer side + /* READ_ONCE() to load read pointer on writer side * this pairs with smp_store_release() in dvb_ringbuffer_read(), * dvb_ringbuffer_read_user(), dvb_ringbuffer_flush(), * or dvb_ringbuffer_reset() */ - free = ACCESS_ONCE(rbuf->pread) - rbuf->pwrite; + free = READ_ONCE(rbuf->pread) - rbuf->pwrite; if (free <= 0) free += rbuf->size; return free-1; @@ -143,7 +143,7 @@ ssize_t dvb_ringbuffer_read_user(struct dvb_ringbuffer *rbuf, u8 __user *buf, si todo -= split; /* smp_store_release() for read pointer update to ensure * that buf is not overwritten until read is complete, - * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + * this pairs with READ_ONCE() in dvb_ringbuffer_free() */ smp_store_release(&rbuf->pread, 0); } @@ -168,7 +168,7 @@ void dvb_ringbuffer_read(struct dvb_ringbuffer *rbuf, u8 *buf, size_t len) todo -= split; /* smp_store_release() for read pointer update to ensure * that buf is not overwritten until read is complete, - * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + * this pairs with READ_ONCE() in dvb_ringbuffer_free() */ smp_store_release(&rbuf->pread, 0); }