netdev - [PATCH bpf] xsk: fix poll/POLLIN premature returns

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Message-Id: <20180723094303.6632-1-bjorn.topel@gmail.com>
Date:   Mon, 23 Jul 2018 11:43:03 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     bjorn.topel@...il.com, magnus.karlsson@...el.com, ast@...com,
        daniel@...earbox.net, netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        qi.z.zhang@...el.com
Subject: [PATCH bpf] xsk: fix poll/POLLIN premature returns

From: Björn Töpel <bjorn.topel@...el.com>

Polling for the ingress queues relies on reading the producer/consumer
pointers of the Rx queue.

Prior this commit, a cached consumer pointer could be used, instead of
the actual consumer pointer and therefore report POLLIN prematurely.

This patch makes sure that the non-cached consumer pointer is used
instead.

Reported-by: Qi Zhang <qi.z.zhang@...el.com>
Tested-by: Qi Zhang <qi.z.zhang@...el.com>
Fixes: c497176cb2e4 ("xsk: add Rx receive functions and poll support")
Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
---
 net/xdp/xsk_queue.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 52ecaf770642..8a64b150be54 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -250,7 +250,7 @@ static inline bool xskq_full_desc(struct xsk_queue *q)
 
 static inline bool xskq_empty_desc(struct xsk_queue *q)
 {
-	return xskq_nb_free(q, q->prod_tail, 1) == q->nentries;
+	return xskq_nb_free(q, q->prod_tail, q->nentries) == q->nentries;
 }
 
 void xskq_set_umem(struct xsk_queue *q, struct xdp_umem_props *umem_props);
-- 
2.17.1