From:   Trond Myklebust <trondmy@gmail.com>
To:     J Bruce Fields <bfields@fieldses.org>
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH] SUNRPC: Don't allow compiler optimisation of svc_xprt_release_slot()
Date:   Thu,  3 Jan 2019 09:17:12 -0500
Message-Id: <20190103141712.24381-1-trond.myklebust@hammerspace.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

Use READ_ONCE() to tell the compiler to not optimse away the read of
xprt->xpt_flags in svc_xprt_release_slot().

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 net/sunrpc/svc_xprt.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 51d36230b6e3..94d344325e22 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -363,9 +363,11 @@ static void svc_xprt_release_slot(struct svc_rqst *rqstp)
 
 static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt)
 {
-	if (xprt->xpt_flags & ((1<<XPT_CONN)|(1<<XPT_CLOSE)))
+	unsigned long xpt_flags = READ_ONCE(xprt->xpt_flags);
+
+	if (xpt_flags & (BIT(XPT_CONN) | BIT(XPT_CLOSE)))
 		return true;
-	if (xprt->xpt_flags & ((1<<XPT_DATA)|(1<<XPT_DEFERRED))) {
+	if (xpt_flags & (BIT(XPT_DATA) | BIT(XPT_DEFERRED))) {
 		if (xprt->xpt_ops->xpo_has_wspace(xprt) &&
 		    svc_xprt_slots_in_range(xprt))
 			return true;
-- 
2.20.1