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From:   Vivek Goyal <vgoyal@redhat.com>
To:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     vgoyal@redhat.com, miklos@szeredi.hu, stefanha@redhat.com,
        dgilbert@redhat.com, sweil@redhat.com, swhiteho@redhat.com
Subject: [PATCH 03/52] fuse: rely on mutex_unlock() barrier instead of fput()
Date:   Mon, 10 Dec 2018 12:12:29 -0500
Message-Id: <20181210171318.16998-4-vgoyal@redhat.com>
In-Reply-To: <20181210171318.16998-1-vgoyal@redhat.com>
References: <20181210171318.16998-1-vgoyal@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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From: Stefan Hajnoczi <stefanha@redhat.com>

fput() will be moved out of this function in a later patch, so we cannot
rely on it as the memory barrier for ensuring file->private_data = fud
is visible.

Luckily there is a mutex_unlock() right before fput() which provides the
same effect.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 fs/fuse/inode.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 0b94b23b02d4..d08cd8bf7705 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1198,12 +1198,11 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 	list_add_tail(&fc->entry, &fuse_conn_list);
 	sb->s_root = root_dentry;
 	file->private_data = fud;
-	mutex_unlock(&fuse_mutex);
 	/*
-	 * atomic_dec_and_test() in fput() provides the necessary
-	 * memory barrier for file->private_data to be visible on all
-	 * CPUs after this
+	 * mutex_unlock() provides the necessary memory barrier for
+	 * file->private_data to be visible on all CPUs after this
 	 */
+	mutex_unlock(&fuse_mutex);
 	fput(file);
 
 	fuse_send_init(fc, init_req);
-- 
2.13.6