Message-ID: <66ec149daf042_2deb5229470@willemb.c.googlers.com.notmuch>
Date: Thu, 19 Sep 2024 08:10:05 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: greearb@...delatech.com, 
 netdev@...r.kernel.org
Cc: Ben Greear <greearb@...delatech.com>
Subject: Re: [PATCH] af_packet:  Fix softirq mismatch in tpacket_rcv

greearb@ wrote:
> From: Ben Greear <greearb@...delatech.com>
> 
> tpacket_rcv can be called from softirq context on input
> path from NIC to stack.  And also called on transmit path
> when sniffing is enabled.  So, use _bh locks to allow this
> to function properly.

It cannot be as straightforward as that, or we would have seen this
much earlier.

On transmit, packet sockets are intercepted by dev_queue_xmit_nit.
Which is called from __dev_queue_xmit with bottom halfs already
disabled:

        /* Disable soft irqs for various locks below. Also
         * stops preemption for RCU.
         */
        rcu_read_lock_bh();

Also, if this proves a real issue on the socket lock, then it would
apply to packet_rcv and tpacket_rcv equally.

Will need to read up a bit more closely on IN-SOFTIRQ-W vs
SOFTIRQ-ON-W unless someone beats me to it.

But likely this is either a false positive, or something specific to
that tpacket_v3 blk_fill_in_prog_lock. Which does get called also
from a timer.


> Thanks to Johannes Berg for providing some explanation of the cryptic
> lockdep output.
> 
> ================================
> WARNING: inconsistent lock state
> 6.11.0 #1 Tainted: G        W
> --------------------------------
> inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
> btserver/134819 [HC0[0]:SC0[0]:HE1:SE1] takes:
> ffff8882da30c118 (rlock-AF_PACKET){+.?.}-{2:2}, at: tpacket_rcv+0x863/0x3b30
> {IN-SOFTIRQ-W} state was registered at:
>   lock_acquire+0x19a/0x4f0
>   _raw_spin_lock+0x27/0x40
>   packet_rcv+0xa33/0x1320
>   __netif_receive_skb_core.constprop.0+0xcb0/0x3a90
>   __netif_receive_skb_list_core+0x2c9/0x890
>   netif_receive_skb_list_internal+0x610/0xcc0
>   napi_complete_done+0x1c0/0x7c0
>   igb_poll+0x1dbb/0x57e0 [igb]
>   __napi_poll.constprop.0+0x99/0x430
>   net_rx_action+0x8e7/0xe10
>   handle_softirqs+0x1b7/0x800
>   __irq_exit_rcu+0x91/0xc0
>   irq_exit_rcu+0x5/0x10
>   common_interrupt+0x7f/0xa0
>   asm_common_interrupt+0x22/0x40
>   cpuidle_enter_state+0x289/0x320
>   cpuidle_enter+0x45/0xa0
>   do_idle+0x2fe/0x3e0
>   cpu_startup_entry+0x4b/0x60
>   start_secondary+0x201/0x280
>   common_startup_64+0x13e/0x148
> irq event stamp: 467094363
> hardirqs last  enabled at (467094363): [<ffffffff83dc794b>] _raw_spin_unlock_irqrestore+0x2b/0x50
> hardirqs last disabled at (467094362): [<ffffffff83dc7753>] _raw_spin_lock_irqsave+0x53/0x60
> softirqs last  enabled at (467094360): [<ffffffff83481213>] skb_attempt_defer_free+0x303/0x4e0
> softirqs last disabled at (467094358): [<ffffffff83481188>] skb_attempt_defer_free+0x278/0x4e0
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(rlock-AF_PACKET);
>   <Interrupt>
>     lock(rlock-AF_PACKET);
> 
>  *** DEADLOCK ***
> 
> 3 locks held by btserver/134819:
>  #0: ffff888136a3bf98 (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_recvmsg+0xc7/0x4e0
>  #1: ffffffff84e4bc20 (rcu_read_lock){....}-{1:2}, at: __ip_queue_xmit+0x59/0x1e20
>  #2: ffffffff84e4bc20 (rcu_read_lock){....}-{1:2}, at: dev_queue_xmit_nit+0x2a/0xa40
> 
> stack backtrace:
> CPU: 2 UID: 0 PID: 134819 Comm: btserver Tainted: G        W          6.11.0 #1
> Tainted: [W]=WARN
> Hardware name: Default string Default string/SKYBAY, BIOS 5.12 08/04/2020
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x73/0xa0
>  mark_lock+0x102e/0x16b0
>  ? print_usage_bug.part.0+0x600/0x600
>  ? print_usage_bug.part.0+0x600/0x600
>  ? print_usage_bug.part.0+0x600/0x600
>  ? lock_acquire+0x19a/0x4f0
>  ? find_held_lock+0x2d/0x110
>  __lock_acquire+0x9ae/0x6170
>  ? lockdep_hardirqs_on_prepare+0x3e0/0x3e0
>  ? lockdep_hardirqs_on_prepare+0x3e0/0x3e0
>  lock_acquire+0x19a/0x4f0
>  ? tpacket_rcv+0x863/0x3b30
>  ? run_filter+0x131/0x300
>  ? lock_sync+0x170/0x170
>  ? do_syscall_64+0x69/0x160
>  ? entry_SYSCALL_64_after_hwframe+0x4b/0x53
>  ? lock_is_held_type+0xa5/0x110
>  _raw_spin_lock+0x27/0x40
>  ? tpacket_rcv+0x863/0x3b30
>  tpacket_rcv+0x863/0x3b30
>  ? packet_recvmsg+0x1340/0x1340
>  ? __asan_memcpy+0x38/0x60
>  ? __skb_clone+0x547/0x730
>  ? packet_recvmsg+0x1340/0x1340
>  dev_queue_xmit_nit+0x709/0xa40
>  ? lockdep_hardirqs_on_prepare+0x3e0/0x3e0
>  vrf_finish_direct+0x26e/0x340 [vrf]
>  ? vrf_ip_local_out+0x570/0x570 [vrf]
>  vrf_l3_out+0x5f4/0xe80 [vrf]
>  __ip_local_out+0x51e/0x7a0
>  ? __ip_append_data+0x3d00/0x3d00
>  ? __lock_acquire+0x1b57/0x6170
>  ? ipv4_dst_check+0xd6/0x150
>  ? lock_is_held_type+0xa5/0x110
>  __ip_queue_xmit+0x7ff/0x1e20
>  __tcp_transmit_skb+0x1699/0x3850
>  ? __tcp_select_window+0xfb0/0xfb0
>  ? __build_skb_around+0x22f/0x330
>  ? __alloc_skb+0x13d/0x2c0
>  ? __napi_build_skb+0x40/0x40
>  ? __tcp_send_ack.part.0+0x5f/0x690
>  ? skb_attempt_defer_free+0x303/0x4e0
>  tcp_recvmsg_locked+0xdd1/0x23e0
>  ? tcp_recvmsg+0xc7/0x4e0
>  ? tcp_update_recv_tstamps+0x1c0/0x1c0
>  tcp_recvmsg+0xe5/0x4e0
>  ? tcp_recv_timestamp+0x6c0/0x6c0
>  inet_recvmsg+0xf0/0x4b0
>  ? inet_splice_eof+0xa0/0xa0
>  ? inet_splice_eof+0xa0/0xa0
>  sock_recvmsg+0xc8/0x150
>  ? poll_schedule_timeout.constprop.0+0xe0/0xe0
>  sock_read_iter+0x258/0x380
>  ? poll_schedule_timeout.constprop.0+0xe0/0xe0
>  ? sock_recvmsg+0x150/0x150
>  ? rw_verify_area+0x64/0x590
>  vfs_read+0x8d5/0xc20
>  ? poll_schedule_timeout.constprop.0+0xe0/0xe0
>  ? kernel_read+0x50/0x50
>  ? __asan_memset+0x1f/0x40
>  ? ktime_get_ts64+0x85/0x210
>  ? __fget_light+0x4d/0x1d0
>  ksys_read+0x166/0x1c0
>  ? __ia32_sys_pwrite64+0x1d0/0x1d0
>  ? __ia32_sys_poll+0x3e0/0x3e0
>  do_syscall_64+0x69/0x160
>  entry_SYSCALL_64_after_hwframe+0x4b/0x53
> RIP: 0033:0x7f6909b01b92
> 
> Signed-off-by: Ben Greear <greearb@...delatech.com>
> ---
>  net/packet/af_packet.c | 22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 4692a9ef110b..17f9e2efdf25 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -760,8 +760,8 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
>  	 */
>  	if (BLOCK_NUM_PKTS(pbd)) {
>  		/* Waiting for skb_copy_bits to finish... */
> -		write_lock(&pkc->blk_fill_in_prog_lock);
> -		write_unlock(&pkc->blk_fill_in_prog_lock);
> +		write_lock_bh(&pkc->blk_fill_in_prog_lock);
> +		write_unlock_bh(&pkc->blk_fill_in_prog_lock);
>  	}
>  
>  	if (pkc->last_kactive_blk_num == pkc->kactive_blk_num) {
> @@ -1021,8 +1021,8 @@ static void prb_retire_current_block(struct tpacket_kbdq_core *pkc,
>  		 */
>  		if (!(status & TP_STATUS_BLK_TMO)) {
>  			/* Waiting for skb_copy_bits to finish... */
> -			write_lock(&pkc->blk_fill_in_prog_lock);
> -			write_unlock(&pkc->blk_fill_in_prog_lock);
> +			write_lock_bh(&pkc->blk_fill_in_prog_lock);
> +			write_unlock_bh(&pkc->blk_fill_in_prog_lock);
>  		}
>  		prb_close_block(pkc, pbd, po, status);
>  		return;
> @@ -1044,7 +1044,7 @@ static void prb_clear_blk_fill_status(struct packet_ring_buffer *rb)
>  {
>  	struct tpacket_kbdq_core *pkc  = GET_PBDQC_FROM_RB(rb);
>  
> -	read_unlock(&pkc->blk_fill_in_prog_lock);
> +	read_unlock_bh(&pkc->blk_fill_in_prog_lock);
>  }
>  
>  static void prb_fill_rxhash(struct tpacket_kbdq_core *pkc,
> @@ -1105,7 +1105,7 @@ static void prb_fill_curr_block(char *curr,
>  	pkc->nxt_offset += TOTAL_PKT_LEN_INCL_ALIGN(len);
>  	BLOCK_LEN(pbd) += TOTAL_PKT_LEN_INCL_ALIGN(len);
>  	BLOCK_NUM_PKTS(pbd) += 1;
> -	read_lock(&pkc->blk_fill_in_prog_lock);
> +	read_lock_bh(&pkc->blk_fill_in_prog_lock);
>  	prb_run_all_ft_ops(pkc, ppd);
>  }
>  
> @@ -2413,7 +2413,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  			vnet_hdr_sz = 0;
>  		}
>  	}
> -	spin_lock(&sk->sk_receive_queue.lock);
> +	spin_lock_bh(&sk->sk_receive_queue.lock);
>  	h.raw = packet_current_rx_frame(po, skb,
>  					TP_STATUS_KERNEL, (macoff+snaplen));
>  	if (!h.raw)
> @@ -2453,7 +2453,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  		skb_clear_delivery_time(copy_skb);
>  		__skb_queue_tail(&sk->sk_receive_queue, copy_skb);
>  	}
> -	spin_unlock(&sk->sk_receive_queue.lock);
> +	spin_unlock_bh(&sk->sk_receive_queue.lock);
>  
>  	skb_copy_bits(skb, 0, h.raw + macoff, snaplen);
>  
> @@ -2546,10 +2546,10 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  #endif
>  
>  	if (po->tp_version <= TPACKET_V2) {
> -		spin_lock(&sk->sk_receive_queue.lock);
> +		spin_lock_bh(&sk->sk_receive_queue.lock);
>  		__packet_set_status(po, h.raw, status);
>  		__clear_bit(slot_id, po->rx_ring.rx_owner_map);
> -		spin_unlock(&sk->sk_receive_queue.lock);
> +		spin_unlock_bh(&sk->sk_receive_queue.lock);
>  		sk->sk_data_ready(sk);
>  	} else if (po->tp_version == TPACKET_V3) {
>  		prb_clear_blk_fill_status(&po->rx_ring);
> @@ -2565,7 +2565,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  	return 0;
>  
>  drop_n_account:
> -	spin_unlock(&sk->sk_receive_queue.lock);
> +	spin_unlock_bh(&sk->sk_receive_queue.lock);
>  	atomic_inc(&po->tp_drops);
>  	drop_reason = SKB_DROP_REASON_PACKET_SOCK_ERROR;
>  
> -- 
> 2.42.0
> 

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