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Subject[PATCH 1/2] tty: Replace smp_rmb/smp_wmb with smp_load_acquire/smp_store_release
Date
Clarify flip buffer producer/consumer operation; the use of
smp_load_acquire() and smp_store_release() more clearly indicates
which memory access requires a barrier.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
drivers/tty/tty_buffer.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 4cf263d..25ba5af 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -291,12 +291,11 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size,
n->flags = flags;
buf->tail = n;
b->commit = b->used;
- /* paired w/ barrier in flush_to_ldisc(); ensures the
+ /* paired w/ acquire in flush_to_ldisc(); ensures the
* latest commit value can be read before the head is
* advanced to the next buffer
*/
- smp_wmb();
- b->next = n;
+ smp_store_release(&b->next, n);
} else if (change)
size = 0;
else
@@ -488,12 +487,11 @@ static void flush_to_ldisc(struct work_struct *work)
if (atomic_read(&buf->priority))
break;

- next = head->next;
- /* paired w/ barrier in __tty_buffer_request_room();
+ /* paired w/ release in __tty_buffer_request_room();
* ensures commit value read is not stale if the head
* is advancing to the next buffer
*/
- smp_rmb();
+ next = smp_load_acquire(&head->next);
count = head->commit - head->read;
if (!count) {
if (next == NULL) {
--
2.4.5


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