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ppp: Fix race condition with queue start/stop

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Commit e675f0cc9a ("ppp: Don't stop and
restart queue on every TX packet") introduced a race condition which
could leave the net queue stopped even when the channel is no longer
busy. By calling netif_stop_queue() from ppp_start_xmit(), based on the
return value from ppp_xmit_process() but *after* all the locks have been
dropped, we could potentially do so *after* the channel has actually
finished transmitting and attempted to re-wake the queue.

Fix this by moving the netif_stop_queue() into ppp_xmit_process() under
the xmit lock. I hadn't done this previously, because it gets called
from other places than ppp_start_xmit(). But I now think it's the better
option. The net queue *should* be stopped if the channel becomes
congested due to writes from pppd, anyway.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Woodhouse 2012-04-08 10:01:44 +00:00 committed by David S. Miller
parent 1716a96101
commit 9a5d2bd99e
1 changed files with 6 additions and 9 deletions
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15
drivers/net/ppp/ppp_generic.c
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@ -235,7 +235,7 @@ struct ppp_net {
/* Prototypes. */
static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
struct file *file, unsigned int cmd, unsigned long arg);
static int ppp_xmit_process(struct ppp *ppp);
static void ppp_xmit_process(struct ppp *ppp);
static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
static void ppp_push(struct ppp *ppp);
static void ppp_channel_push(struct channel *pch);
@ -969,8 +969,7 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
put_unaligned_be16(proto, pp);
skb_queue_tail(&ppp->file.xq, skb);
if (!ppp_xmit_process(ppp))
netif_stop_queue(dev);
ppp_xmit_process(ppp);
return NETDEV_TX_OK;
outf:
@ -1048,11 +1047,10 @@ static void ppp_setup(struct net_device *dev)
* Called to do any work queued up on the transmit side
* that can now be done.
*/
static int
static void
ppp_xmit_process(struct ppp *ppp)
{
struct sk_buff *skb;
int ret = 0;
ppp_xmit_lock(ppp);
if (!ppp->closing) {
@ -1062,13 +1060,12 @@ ppp_xmit_process(struct ppp *ppp)
ppp_send_frame(ppp, skb);
/* If there's no work left to do, tell the core net
code that we can accept some more. */
if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) {
if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
netif_wake_queue(ppp->dev);
ret = 1;
}
else
netif_stop_queue(ppp->dev);
}
ppp_xmit_unlock(ppp);
return ret;
}
static inline struct sk_buff *