linux-kernel - [PATCH 4/6] 9p: Remove an unnecessary memory barrier

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Message-Id: <20180628132629.3148-5-willy@infradead.org>
Date:   Thu, 28 Jun 2018 06:26:27 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     v9fs-developer@...ts.sourceforge.net
Cc:     linux-fsdevel@...r.kernel.org,
        Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>
Subject: [PATCH 4/6] 9p: Remove an unnecessary memory barrier

And add a comment about why we don't need it.

Signed-off-by: Matthew Wilcox <willy@...radead.org>
---
 net/9p/client.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index 602f76de388a..2dce8d8307cc 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -436,13 +436,9 @@ void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status)
 {
 	p9_debug(P9_DEBUG_MUX, " tag %d\n", req->tc->tag);
 
-	/*
-	 * This barrier is needed to make sure any change made to req before
-	 * the other thread wakes up will indeed be seen by the waiting side.
-	 */
-	smp_wmb();
 	req->status = status;
 
+	/* wake_up is an implicit write memory barrier */
 	wake_up(&req->wq);
 	p9_debug(P9_DEBUG_MUX, "wakeup: %d\n", req->tc->tag);
 }
-- 
2.18.0