[V9fs-developer] [PATCH] net/9p: Fix a deadlock case in the virtio transport

[jiangyiwen]

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 <jiangyi...@huawei.com>
---
 net/9p/trans_virtio.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 05006cb..9b0f5f2 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -148,20 +148,18 @@ static void req_done(struct virtqueue *vq)

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

+       spin_lock_irqsave(&chan->lock, flags);
        while (1) {
-               spin_lock_irqsave(&chan->lock, flags);
                req = virtqueue_get_buf(chan->vq, &len);
-               if (req == NULL) {
-                       spin_unlock_irqrestore(&chan->lock, flags);
+               if (req == NULL)
                        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);
                if (len)
                        p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
        }
+       spin_unlock_irqrestore(&chan->lock, flags);
 }

 /**
-- 
1.8.3.1