Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
To:     Andrew Morton <akpm@linux-foundation.org>,
        Eric Van Hensbergen <ericvh@gmail.com>,
        Ron Minnich <rminnich@sandia.gov>,
        Latchesar Ionkov <lucho@ionkov.net>
CC:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        <v9fs-developer@lists.sourceforge.net>,
        Dominique Martinet <asmadeus@codewreck.org>
From:   jiangyiwen <jiangyiwen@huawei.com>
Subject: [V9fs-developer] [PATCH v2] net/9p: Fix a deadlock case in the virtio
 transport
Message-ID: <5B4DCD0A.8040600@huawei.com>
Date:   Tue, 17 Jul 2018 19:03:38 +0800
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101
 Thunderbird/38.5.1
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

When client has multiple threads that issue io requests
all the time, and the server has a very good performance,
it may cause cpu is running in the irq context for a long
time because it can check virtqueue has buf in the *while*
loop.

So we should keep chan->lock in the whole loop.

Signed-off-by: Yiwen Jiang <jiangyiwen@huawei.com>
---
 net/9p/trans_virtio.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 05006cb..e5fea8b 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -148,20 +148,15 @@ static void req_done(struct virtqueue *vq)

 	p9_debug(P9_DEBUG_TRANS, ": request done\n");

-	while (1) {
-		spin_lock_irqsave(&chan->lock, flags);
-		req = virtqueue_get_buf(chan->vq, &len);
-		if (req == NULL) {
-			spin_unlock_irqrestore(&chan->lock, flags);
-			break;
-		}
-		chan->ring_bufs_avail = 1;
-		spin_unlock_irqrestore(&chan->lock, flags);
-		/* Wakeup if anyone waiting for VirtIO ring space. */
-		wake_up(chan->vc_wq);
+	spin_lock_irqsave(&chan->lock, flags);
+	while ((req = virtqueue_get_buf(chan->vq, &len)) != NULL) {
 		if (len)
 			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
 	}
+	chan->ring_bufs_avail = 1;
+	spin_unlock_irqrestore(&chan->lock, flags);
+	/* Wakeup if anyone waiting for VirtIO ring space. */
+	wake_up(chan->vc_wq);
 }

 /**
-- 
1.8.3.1