linux-kernel - [PATCH 3/8] Drivers: hv: vmbus: Use READ_ONCE() to read variables that are volatile

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Message-Id: <1459900667-20367-3-git-send-email-kys@microsoft.com>
Date:	Tue,  5 Apr 2016 16:57:42 -0700
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	vkuznets@...hat.com, jasowang@...hat.com
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 3/8] Drivers: hv: vmbus: Use READ_ONCE() to read variables that are volatile

Use the READ_ONCE macro to access variabes that can change asynchronously.
This is the recommended mechanism for dealing with "unsafe" compiler
optimizations.

Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 drivers/hv/ring_buffer.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 544362c..6ea1b55 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -69,7 +69,7 @@ u32 hv_end_read(struct hv_ring_buffer_info *rbi)
 static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
 {
 	mb();
-	if (rbi->ring_buffer->interrupt_mask)
+	if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
 		return false;
 
 	/* check interrupt_mask before read_index */
@@ -78,7 +78,7 @@ static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
 	 * This is the only case we need to signal when the
 	 * ring transitions from being empty to non-empty.
 	 */
-	if (old_write == rbi->ring_buffer->read_index)
+	if (old_write == READ_ONCE(rbi->ring_buffer->read_index))
 		return true;
 
 	return false;
@@ -117,7 +117,7 @@ static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
 	 */
 	mb();
 
-	pending_sz = rbi->ring_buffer->pending_send_sz;
+	pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
 	/* If the other end is not blocked on write don't bother. */
 	if (pending_sz == 0)
 		return false;
-- 
1.7.4.1