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

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Date:   Sat, 14 Jul 2018 16:48:15 +0800
From:   jiangyiwen <jiangyiwen@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <v9fs-developer@...ts.sourceforge.net>,
        Dominique Martinet <asmadeus@...ewreck.org>
Subject: [V9fs-developer] [PATCH] net/9p: Fix a deadlock case in the virtio
 transport

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@...wei.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