Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752070AbdLET3n (ORCPT ); Tue, 5 Dec 2017 14:29:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38084 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751888AbdLET3j (ORCPT ); Tue, 5 Dec 2017 14:29:39 -0500 Date: Tue, 5 Dec 2017 21:29:37 +0200 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: George Cherian , Jason Wang , davem@davemloft.net, edumazet@google.com, netdev@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: [PATCH] ptr_ring: add barriers Message-ID: <1512501990-30029-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Mutt-Fcc: =sent X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 05 Dec 2017 19:29:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2062 Lines: 64 Users of ptr_ring expect that it's safe to give the data structure a pointer and have it be available to consumers, but that actually requires an smb_wmb or a stronger barrier. In absence of such barriers and on architectures that reorder writes, consumer might read an un=initialized value from an skb pointer stored in the skb array. This was observed causing crashes. To fix, add memory barriers. The barrier we use is a wmb, the assumption being that producers do not need to read the value so we do not need to order these reads. Reported-by: George Cherian Suggested-by: Jason Wang Signed-off-by: Michael S. Tsirkin --- George, could you pls report whether this patch fixes the issue for you? This seems to be needed in stable as well. include/linux/ptr_ring.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index 37b4bb2..6866df4 100644 --- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r) /* Note: callers invoking this in a loop must use a compiler barrier, * for example cpu_relax(). Callers must hold producer_lock. + * Callers are responsible for making sure pointer that is being queued + * points to a valid data. */ static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr) { if (unlikely(!r->size) || r->queue[r->producer]) return -ENOSPC; + /* Make sure the pointer we are storing points to a valid data. */ + /* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */ + smp_wmb(); + r->queue[r->producer++] = ptr; if (unlikely(r->producer >= r->size)) r->producer = 0; @@ -275,6 +281,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r) if (ptr) __ptr_ring_discard_one(r); + /* Make sure anyone accessing data through the pointer is up to date. */ + /* Pairs with smp_wmb in __ptr_ring_produce. */ + smp_read_barrier_depends(); return ptr; } -- MST