linux-kernel - [PATCH] tun: don't look at current when non-blocking

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Message-ID: <20131006182512.GA16504@redhat.com>
Date:	Sun, 6 Oct 2013 21:25:12 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	Jason Wang <jasowang@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: [PATCH] tun: don't look at current when non-blocking

We play with a wait queue even if socket is
non blocking. This is an obvious waste.
Besides, it will prevent calling the non blocking
variant when current is not valid.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/net/tun.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 807815f..7cb105c 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1293,7 +1293,8 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
 	if (unlikely(!noblock))
 		add_wait_queue(&tfile->wq.wait, &wait);
 	while (len) {
-		current->state = TASK_INTERRUPTIBLE;
+		if (unlikely(!noblock))
+			current->state = TASK_INTERRUPTIBLE;
 
 		/* Read frames from the queue */
 		if (!(skb = skb_dequeue(&tfile->socket.sk->sk_receive_queue))) {
@@ -1320,9 +1321,10 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
 		break;
 	}
 
-	current->state = TASK_RUNNING;
-	if (unlikely(!noblock))
+	if (unlikely(!noblock)) {
+		current->state = TASK_RUNNING;
 		remove_wait_queue(&tfile->wq.wait, &wait);
+	}
 
 	return ret;
 }
-- 
MST
--
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