ppp: annotate lockless queue empty check

[PATCH net] ppp: annotate lockless queue empty check

Posted by Qingfang Deng 1 month, 2 weeks ago

ppp_poll() checks whether pf->rq contains a packet without holding the
queue lock. skb_peek() requires appropriate locking or a private queue,
neither of which applies because ppp_input() can enqueue concurrently.

Only queue emptiness is needed, so use skb_queue_empty_lockless()
instead.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
---
 drivers/net/ppp/ppp_generic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index e1013621eb1d..1a610a18893b 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -556,7 +556,7 @@ static __poll_t ppp_poll(struct file *file, poll_table *wait)
 		return 0;
 	poll_wait(file, &pf->rwait, wait);
 	mask = EPOLLOUT | EPOLLWRNORM;
-	if (skb_peek(&pf->rq))
+	if (!skb_queue_empty_lockless(&pf->rq))
 		mask |= EPOLLIN | EPOLLRDNORM;
 	if (pf->dead)
 		mask |= EPOLLHUP;
-- 
2.43.0

Re: [PATCH net] ppp: annotate lockless queue empty check

Posted by Breno Leitao 1 month, 2 weeks ago

On Tue, Aug 11, 2026 at 02:02:29PM +0800, Qingfang Deng wrote:
> ppp_poll() checks whether pf->rq contains a packet without holding the
> queue lock. skb_peek() requires appropriate locking or a private queue,
> neither of which applies because ppp_input() can enqueue concurrently.
> 
> Only queue emptiness is needed, so use skb_queue_empty_lockless()
> instead.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>

Reviewed-by: Breno Leitao <leitao@debian.org.