Date: Thu, 26 Oct 2023 13:21:24 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org,
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next] virtio_net: use u64_stats_t infra to avoid
 data-races

On Thu, Oct 26, 2023 at 05:18:40PM +0000, Eric Dumazet wrote:
> syzbot reported a data-race in virtnet_poll / virtnet_stats [1]
> 
> u64_stats_t infra has very nice accessors that must be used
> to avoid potential load-store tearing.
> 
> [1]
> BUG: KCSAN: data-race in virtnet_poll / virtnet_stats
> 
> read-write to 0xffff88810271b1a0 of 8 bytes by interrupt on cpu 0:
> virtnet_receive drivers/net/virtio_net.c:2102 [inline]
> virtnet_poll+0x6c8/0xb40 drivers/net/virtio_net.c:2148
> __napi_poll+0x60/0x3b0 net/core/dev.c:6527
> napi_poll net/core/dev.c:6594 [inline]
> net_rx_action+0x32b/0x750 net/core/dev.c:6727
> __do_softirq+0xc1/0x265 kernel/softirq.c:553
> invoke_softirq kernel/softirq.c:427 [inline]
> __irq_exit_rcu kernel/softirq.c:632 [inline]
> irq_exit_rcu+0x3b/0x90 kernel/softirq.c:644
> common_interrupt+0x7f/0x90 arch/x86/kernel/irq.c:247
> asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:636
> __sanitizer_cov_trace_const_cmp8+0x0/0x80 kernel/kcov.c:306
> jbd2_write_access_granted fs/jbd2/transaction.c:1174 [inline]
> jbd2_journal_get_write_access+0x94/0x1c0 fs/jbd2/transaction.c:1239
> __ext4_journal_get_write_access+0x154/0x3f0 fs/ext4/ext4_jbd2.c:241
> ext4_reserve_inode_write+0x14e/0x200 fs/ext4/inode.c:5745
> __ext4_mark_inode_dirty+0x8e/0x440 fs/ext4/inode.c:5919
> ext4_evict_inode+0xaf0/0xdc0 fs/ext4/inode.c:299
> evict+0x1aa/0x410 fs/inode.c:664
> iput_final fs/inode.c:1775 [inline]
> iput+0x42c/0x5b0 fs/inode.c:1801
> do_unlinkat+0x2b9/0x4f0 fs/namei.c:4405
> __do_sys_unlink fs/namei.c:4446 [inline]
> __se_sys_unlink fs/namei.c:4444 [inline]
> __x64_sys_unlink+0x30/0x40 fs/namei.c:4444
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> read to 0xffff88810271b1a0 of 8 bytes by task 2814 on cpu 1:
> virtnet_stats+0x1b3/0x340 drivers/net/virtio_net.c:2564
> dev_get_stats+0x6d/0x860 net/core/dev.c:10511
> rtnl_fill_stats+0x45/0x320 net/core/rtnetlink.c:1261
> rtnl_fill_ifinfo+0xd0e/0x1120 net/core/rtnetlink.c:1867
> rtnl_dump_ifinfo+0x7f9/0xc20 net/core/rtnetlink.c:2240
> netlink_dump+0x390/0x720 net/netlink/af_netlink.c:2266
> netlink_recvmsg+0x425/0x780 net/netlink/af_netlink.c:1992
> sock_recvmsg_nosec net/socket.c:1027 [inline]
> sock_recvmsg net/socket.c:1049 [inline]
> ____sys_recvmsg+0x156/0x310 net/socket.c:2760
> ___sys_recvmsg net/socket.c:2802 [inline]
> __sys_recvmsg+0x1ea/0x270 net/socket.c:2832
> __do_sys_recvmsg net/socket.c:2842 [inline]
> __se_sys_recvmsg net/socket.c:2839 [inline]
> __x64_sys_recvmsg+0x46/0x50 net/socket.c:2839
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> value changed: 0x000000000045c334 -> 0x000000000045c376
> 
> Fixes: 3fa2a1df9094 ("virtio-net: per cpu 64 bit stats (v2)")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Okay then

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/net/virtio_net.c | 124 ++++++++++++++++++++-------------------
>  1 file changed, 65 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 62962216b80c1537b06c1154315c8cd1c9c33413..d16f592c2061fad0414ed893672f91b7813c6423 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -81,24 +81,24 @@ struct virtnet_stat_desc {
>  
>  struct virtnet_sq_stats {
>  	struct u64_stats_sync syncp;
> -	u64 packets;
> -	u64 bytes;
> -	u64 xdp_tx;
> -	u64 xdp_tx_drops;
> -	u64 kicks;
> -	u64 tx_timeouts;
> +	u64_stats_t packets;
> +	u64_stats_t bytes;
> +	u64_stats_t xdp_tx;
> +	u64_stats_t xdp_tx_drops;
> +	u64_stats_t kicks;
> +	u64_stats_t tx_timeouts;
>  };
>  
>  struct virtnet_rq_stats {
>  	struct u64_stats_sync syncp;
> -	u64 packets;
> -	u64 bytes;
> -	u64 drops;
> -	u64 xdp_packets;
> -	u64 xdp_tx;
> -	u64 xdp_redirects;
> -	u64 xdp_drops;
> -	u64 kicks;
> +	u64_stats_t packets;
> +	u64_stats_t bytes;
> +	u64_stats_t drops;
> +	u64_stats_t xdp_packets;
> +	u64_stats_t xdp_tx;
> +	u64_stats_t xdp_redirects;
> +	u64_stats_t xdp_drops;
> +	u64_stats_t kicks;
>  };
>  
>  #define VIRTNET_SQ_STAT(m)	offsetof(struct virtnet_sq_stats, m)
> @@ -775,8 +775,8 @@ static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
>  		return;
>  
>  	u64_stats_update_begin(&sq->stats.syncp);
> -	sq->stats.bytes += bytes;
> -	sq->stats.packets += packets;
> +	u64_stats_add(&sq->stats.bytes, bytes);
> +	u64_stats_add(&sq->stats.packets, packets);
>  	u64_stats_update_end(&sq->stats.syncp);
>  }
>  
> @@ -975,11 +975,11 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>  	}
>  out:
>  	u64_stats_update_begin(&sq->stats.syncp);
> -	sq->stats.bytes += bytes;
> -	sq->stats.packets += packets;
> -	sq->stats.xdp_tx += n;
> -	sq->stats.xdp_tx_drops += n - nxmit;
> -	sq->stats.kicks += kicks;
> +	u64_stats_add(&sq->stats.bytes, bytes);
> +	u64_stats_add(&sq->stats.packets, packets);
> +	u64_stats_add(&sq->stats.xdp_tx, n);
> +	u64_stats_add(&sq->stats.xdp_tx_drops, n - nxmit);
> +	u64_stats_add(&sq->stats.kicks, kicks);
>  	u64_stats_update_end(&sq->stats.syncp);
>  
>  	virtnet_xdp_put_sq(vi, sq);
> @@ -1011,14 +1011,14 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>  	u32 act;
>  
>  	act = bpf_prog_run_xdp(xdp_prog, xdp);
> -	stats->xdp_packets++;
> +	u64_stats_inc(&stats->xdp_packets);
>  
>  	switch (act) {
>  	case XDP_PASS:
>  		return act;
>  
>  	case XDP_TX:
> -		stats->xdp_tx++;
> +		u64_stats_inc(&stats->xdp_tx);
>  		xdpf = xdp_convert_buff_to_frame(xdp);
>  		if (unlikely(!xdpf)) {
>  			netdev_dbg(dev, "convert buff to frame failed for xdp\n");
> @@ -1036,7 +1036,7 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>  		return act;
>  
>  	case XDP_REDIRECT:
> -		stats->xdp_redirects++;
> +		u64_stats_inc(&stats->xdp_redirects);
>  		err = xdp_do_redirect(dev, xdp, xdp_prog);
>  		if (err)
>  			return XDP_DROP;
> @@ -1232,9 +1232,9 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>  	return skb;
>  
>  err_xdp:
> -	stats->xdp_drops++;
> +	u64_stats_inc(&stats->xdp_drops);
>  err:
> -	stats->drops++;
> +	u64_stats_inc(&stats->drops);
>  	put_page(page);
>  xdp_xmit:
>  	return NULL;
> @@ -1253,7 +1253,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  	struct sk_buff *skb;
>  
>  	len -= vi->hdr_len;
> -	stats->bytes += len;
> +	u64_stats_add(&stats->bytes, len);
>  
>  	if (unlikely(len > GOOD_PACKET_LEN)) {
>  		pr_debug("%s: rx error: len %u exceeds max size %d\n",
> @@ -1282,7 +1282,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  		return skb;
>  
>  err:
> -	stats->drops++;
> +	u64_stats_inc(&stats->drops);
>  	put_page(page);
>  	return NULL;
>  }
> @@ -1298,14 +1298,14 @@ static struct sk_buff *receive_big(struct net_device *dev,
>  	struct sk_buff *skb =
>  		page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, 0);
>  
> -	stats->bytes += len - vi->hdr_len;
> +	u64_stats_add(&stats->bytes, len - vi->hdr_len);
>  	if (unlikely(!skb))
>  		goto err;
>  
>  	return skb;
>  
>  err:
> -	stats->drops++;
> +	u64_stats_inc(&stats->drops);
>  	give_pages(rq, page);
>  	return NULL;
>  }
> @@ -1326,7 +1326,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
>  			DEV_STATS_INC(dev, rx_length_errors);
>  			break;
>  		}
> -		stats->bytes += len;
> +		u64_stats_add(&stats->bytes, len);
>  		page = virt_to_head_page(buf);
>  		put_page(page);
>  	}
> @@ -1436,7 +1436,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>  			goto err;
>  		}
>  
> -		stats->bytes += len;
> +		u64_stats_add(&stats->bytes, len);
>  		page = virt_to_head_page(buf);
>  		offset = buf - page_address(page);
>  
> @@ -1600,8 +1600,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>  	put_page(page);
>  	mergeable_buf_free(rq, num_buf, dev, stats);
>  
> -	stats->xdp_drops++;
> -	stats->drops++;
> +	u64_stats_inc(&stats->xdp_drops);
> +	u64_stats_inc(&stats->drops);
>  	return NULL;
>  }
>  
> @@ -1625,7 +1625,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
>  
>  	head_skb = NULL;
> -	stats->bytes += len - vi->hdr_len;
> +	u64_stats_add(&stats->bytes, len - vi->hdr_len);
>  
>  	if (unlikely(len > truesize - room)) {
>  		pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> @@ -1666,7 +1666,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			goto err_buf;
>  		}
>  
> -		stats->bytes += len;
> +		u64_stats_add(&stats->bytes, len);
>  		page = virt_to_head_page(buf);
>  
>  		truesize = mergeable_ctx_to_truesize(ctx);
> @@ -1718,7 +1718,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  	mergeable_buf_free(rq, num_buf, dev, stats);
>  
>  err_buf:
> -	stats->drops++;
> +	u64_stats_inc(&stats->drops);
>  	dev_kfree_skb(head_skb);
>  	return NULL;
>  }
> @@ -1985,7 +1985,7 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
>  		unsigned long flags;
>  
>  		flags = u64_stats_update_begin_irqsave(&rq->stats.syncp);
> -		rq->stats.kicks++;
> +		u64_stats_inc(&rq->stats.kicks);
>  		u64_stats_update_end_irqrestore(&rq->stats.syncp, flags);
>  	}
>  
> @@ -2065,22 +2065,23 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>  	struct virtnet_info *vi = rq->vq->vdev->priv;
>  	struct virtnet_rq_stats stats = {};
>  	unsigned int len;
> +	int packets = 0;
>  	void *buf;
>  	int i;
>  
>  	if (!vi->big_packets || vi->mergeable_rx_bufs) {
>  		void *ctx;
>  
> -		while (stats.packets < budget &&
> +		while (packets < budget &&
>  		       (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
>  			receive_buf(vi, rq, buf, len, ctx, xdp_xmit, &stats);
> -			stats.packets++;
> +			packets++;
>  		}
>  	} else {
> -		while (stats.packets < budget &&
> +		while (packets < budget &&
>  		       (buf = virtnet_rq_get_buf(rq, &len, NULL)) != NULL) {
>  			receive_buf(vi, rq, buf, len, NULL, xdp_xmit, &stats);
> -			stats.packets++;
> +			packets++;
>  		}
>  	}
>  
> @@ -2093,17 +2094,19 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>  		}
>  	}
>  
> +	u64_stats_set(&stats.packets, packets);
>  	u64_stats_update_begin(&rq->stats.syncp);
>  	for (i = 0; i < VIRTNET_RQ_STATS_LEN; i++) {
>  		size_t offset = virtnet_rq_stats_desc[i].offset;
> -		u64 *item;
> +		u64_stats_t *item, *src;
>  
> -		item = (u64 *)((u8 *)&rq->stats + offset);
> -		*item += *(u64 *)((u8 *)&stats + offset);
> +		item = (u64_stats_t *)((u8 *)&rq->stats + offset);
> +		src = (u64_stats_t *)((u8 *)&stats + offset);
> +		u64_stats_add(item, u64_stats_read(src));
>  	}
>  	u64_stats_update_end(&rq->stats.syncp);
>  
> -	return stats.packets;
> +	return packets;
>  }
>  
>  static void virtnet_poll_cleantx(struct receive_queue *rq)
> @@ -2158,7 +2161,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
>  		sq = virtnet_xdp_get_sq(vi);
>  		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
>  			u64_stats_update_begin(&sq->stats.syncp);
> -			sq->stats.kicks++;
> +			u64_stats_inc(&sq->stats.kicks);
>  			u64_stats_update_end(&sq->stats.syncp);
>  		}
>  		virtnet_xdp_put_sq(vi, sq);
> @@ -2370,7 +2373,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>  	if (kick || netif_xmit_stopped(txq)) {
>  		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
>  			u64_stats_update_begin(&sq->stats.syncp);
> -			sq->stats.kicks++;
> +			u64_stats_inc(&sq->stats.kicks);
>  			u64_stats_update_end(&sq->stats.syncp);
>  		}
>  	}
> @@ -2553,16 +2556,16 @@ static void virtnet_stats(struct net_device *dev,
>  
>  		do {
>  			start = u64_stats_fetch_begin(&sq->stats.syncp);
> -			tpackets = sq->stats.packets;
> -			tbytes   = sq->stats.bytes;
> -			terrors  = sq->stats.tx_timeouts;
> +			tpackets = u64_stats_read(&sq->stats.packets);
> +			tbytes   = u64_stats_read(&sq->stats.bytes);
> +			terrors  = u64_stats_read(&sq->stats.tx_timeouts);
>  		} while (u64_stats_fetch_retry(&sq->stats.syncp, start));
>  
>  		do {
>  			start = u64_stats_fetch_begin(&rq->stats.syncp);
> -			rpackets = rq->stats.packets;
> -			rbytes   = rq->stats.bytes;
> -			rdrops   = rq->stats.drops;
> +			rpackets = u64_stats_read(&rq->stats.packets);
> +			rbytes   = u64_stats_read(&rq->stats.bytes);
> +			rdrops   = u64_stats_read(&rq->stats.drops);
>  		} while (u64_stats_fetch_retry(&rq->stats.syncp, start));
>  
>  		tot->rx_packets += rpackets;
> @@ -3191,17 +3194,19 @@ static void virtnet_get_ethtool_stats(struct net_device *dev,
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	unsigned int idx = 0, start, i, j;
>  	const u8 *stats_base;
> +	const u64_stats_t *p;
>  	size_t offset;
>  
>  	for (i = 0; i < vi->curr_queue_pairs; i++) {
>  		struct receive_queue *rq = &vi->rq[i];
>  
> -		stats_base = (u8 *)&rq->stats;
> +		stats_base = (const u8 *)&rq->stats;
>  		do {
>  			start = u64_stats_fetch_begin(&rq->stats.syncp);
>  			for (j = 0; j < VIRTNET_RQ_STATS_LEN; j++) {
>  				offset = virtnet_rq_stats_desc[j].offset;
> -				data[idx + j] = *(u64 *)(stats_base + offset);
> +				p = (const u64_stats_t *)(stats_base + offset);
> +				data[idx + j] = u64_stats_read(p);
>  			}
>  		} while (u64_stats_fetch_retry(&rq->stats.syncp, start));
>  		idx += VIRTNET_RQ_STATS_LEN;
> @@ -3210,12 +3215,13 @@ static void virtnet_get_ethtool_stats(struct net_device *dev,
>  	for (i = 0; i < vi->curr_queue_pairs; i++) {
>  		struct send_queue *sq = &vi->sq[i];
>  
> -		stats_base = (u8 *)&sq->stats;
> +		stats_base = (const u8 *)&sq->stats;
>  		do {
>  			start = u64_stats_fetch_begin(&sq->stats.syncp);
>  			for (j = 0; j < VIRTNET_SQ_STATS_LEN; j++) {
>  				offset = virtnet_sq_stats_desc[j].offset;
> -				data[idx + j] = *(u64 *)(stats_base + offset);
> +				p = (const u64_stats_t *)(stats_base + offset);
> +				data[idx + j] = u64_stats_read(p);
>  			}
>  		} while (u64_stats_fetch_retry(&sq->stats.syncp, start));
>  		idx += VIRTNET_SQ_STATS_LEN;
> @@ -3898,7 +3904,7 @@ static void virtnet_tx_timeout(struct net_device *dev, unsigned int txqueue)
>  	struct netdev_queue *txq = netdev_get_tx_queue(dev, txqueue);
>  
>  	u64_stats_update_begin(&sq->stats.syncp);
> -	sq->stats.tx_timeouts++;
> +	u64_stats_inc(&sq->stats.tx_timeouts);
>  	u64_stats_update_end(&sq->stats.syncp);
>  
>  	netdev_err(dev, "TX timeout on queue: %u, sq: %s, vq: 0x%x, name: %s, %u usecs ago\n",
> -- 
> 2.42.0.758.gaed0368e0e-goog

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