Subject: Re: [PATCH iwl-net v3 2/6] ice: protect XDP configuration with a mutex

From: Maciej Fijalkowski <[email-masked]>
Date: Thu, 22 Aug 2024 13:39:15 +0200

On Mon, Aug 19, 2024 at 12:05:39PM +0200, Larysa Zaremba wrote:
> The main threat to data consistency in ice_xdp() is a possible asynchronous
> PF reset. It can be triggered by a user or by TX timeout handler.
> 
> XDP setup and PF reset code access the same resources in the following
> sections:
> * ice_vsi_close() in ice_prepare_for_reset() - already rtnl-locked
> * ice_vsi_rebuild() for the PF VSI - not protected
> * ice_vsi_open() - already rtnl-locked
> 
> With an unfortunate timing, such accesses can result in a crash such as the
> one below:
> 
> [ +1.999878] ice 0000:b1:00.0: Registered XDP mem model MEM_TYPE_XSK_BUFF_POOL on Rx ring 14
> [ +2.002992] ice 0000:b1:00.0: Registered XDP mem model MEM_TYPE_XSK_BUFF_POOL on Rx ring 18
> [Mar15 18:17] ice 0000:b1:00.0 ens801f0np0: NETDEV WATCHDOG: CPU: 38: transmit queue 14 timed out 80692736 ms
> [ +0.000093] ice 0000:b1:00.0 ens801f0np0: tx_timeout: VSI_num: 6, Q 14, NTC: 0x0, HW_HEAD: 0x0, NTU: 0x0, INT: 0x4000001
> [ +0.000012] ice 0000:b1:00.0 ens801f0np0: tx_timeout recovery level 1, txqueue 14
> [ +0.394718] ice 0000:b1:00.0: PTP reset successful
> [ +0.006184] BUG: kernel NULL pointer dereference, address: 0000000000000098
> [ +0.000045] #PF: supervisor read access in kernel mode
> [ +0.000023] #PF: error_code(0x0000) - not-present page
> [ +0.000023] PGD 0 P4D 0
> [ +0.000018] Oops: 0000 [#1] PREEMPT SMP NOPTI
> [ +0.000023] CPU: 38 PID: 7540 Comm: kworker/38:1 Not tainted 6.8.0-rc7 #1
> [ +0.000031] Hardware name: Intel Corporation S2600WFT/S2600WFT, BIOS SE5C620.86B.02.01.0014.082620210524 08/26/2021
> [ +0.000036] Workqueue: ice ice_service_task [ice]
> [ +0.000183] RIP: 0010:ice_clean_tx_ring+0xa/0xd0 [ice]
> [...]
> [ +0.000013] Call Trace:
> [ +0.000016] <TASK>
> [ +0.000014] ? __die+0x1f/0x70
> [ +0.000029] ? page_fault_oops+0x171/0x4f0
> [ +0.000029] ? schedule+0x3b/0xd0
> [ +0.000027] ? exc_page_fault+0x7b/0x180
> [ +0.000022] ? asm_exc_page_fault+0x22/0x30
> [ +0.000031] ? ice_clean_tx_ring+0xa/0xd0 [ice]
> [ +0.000194] ice_free_tx_ring+0xe/0x60 [ice]
> [ +0.000186] ice_destroy_xdp_rings+0x157/0x310 [ice]
> [ +0.000151] ice_vsi_decfg+0x53/0xe0 [ice]
> [ +0.000180] ice_vsi_rebuild+0x239/0x540 [ice]
> [ +0.000186] ice_vsi_rebuild_by_type+0x76/0x180 [ice]
> [ +0.000145] ice_rebuild+0x18c/0x840 [ice]
> [ +0.000145] ? delay_tsc+0x4a/0xc0
> [ +0.000022] ? delay_tsc+0x92/0xc0
> [ +0.000020] ice_do_reset+0x140/0x180 [ice]
> [ +0.000886] ice_service_task+0x404/0x1030 [ice]
> [ +0.000824] process_one_work+0x171/0x340
> [ +0.000685] worker_thread+0x277/0x3a0
> [ +0.000675] ? preempt_count_add+0x6a/0xa0
> [ +0.000677] ? _raw_spin_lock_irqsave+0x23/0x50
> [ +0.000679] ? __pfx_worker_thread+0x10/0x10
> [ +0.000653] kthread+0xf0/0x120
> [ +0.000635] ? __pfx_kthread+0x10/0x10
> [ +0.000616] ret_from_fork+0x2d/0x50
> [ +0.000612] ? __pfx_kthread+0x10/0x10
> [ +0.000604] ret_from_fork_asm+0x1b/0x30
> [ +0.000604] </TASK>
> 
> The previous way of handling this through returning -EBUSY is not viable,
> particularly when destroying AF_XDP socket, because the kernel proceeds
> with removal anyway.
> 
> There is plenty of code between those calls and there is no need to create
> a large critical section that covers all of them, same as there is no need
> to protect ice_vsi_rebuild() with rtnl_lock().
> 
> Add xdp_state_lock mutex to protect ice_vsi_rebuild() and ice_xdp().
> 
> Leaving unprotected sections in between would result in two states that
> have to be considered:
> 1. when the VSI is closed, but not yet rebuild
> 2. when VSI is already rebuild, but not yet open
> 
> The latter case is actually already handled through !netif_running() case,
> we just need to adjust flag checking a little. The former one is not as
> trivial, because between ice_vsi_close() and ice_vsi_rebuild(), a lot of
> hardware interaction happens, this can make adding/deleting rings exit
> with an error. Luckily, VSI rebuild is pending and can apply new
> configuration for us in a managed fashion.
> 
> Therefore, add an additional VSI state flag ICE_VSI_REBUILD_PENDING to
> indicate that ice_xdp() can just hot-swap the program.
> 
> Also, as ice_vsi_rebuild() flow is touched in this patch, make it more
> consistent by deconfiguring VSI when coalesce allocation fails.
> 
> Fixes: 2d4238f55697 ("ice: Add support for AF_XDP")
> Fixes: efc2214b6047 ("ice: Add support for XDP")
> Reviewed-by: Wojciech Drewek <[email-masked]>
> Reviewed-by: Jacob Keller <[email-masked]>
> Tested-by: Chandan Kumar Rout <[email-masked]>
> Signed-off-by: Larysa Zaremba <[email-masked]>
> ---
>  drivers/net/ethernet/intel/ice/ice.h      |  2 ++
>  drivers/net/ethernet/intel/ice/ice_lib.c  | 34 ++++++++++++++---------
>  drivers/net/ethernet/intel/ice/ice_main.c | 19 +++++++++----
>  drivers/net/ethernet/intel/ice/ice_xsk.c  |  3 +-
>  4 files changed, 39 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice.h b/drivers/net/ethernet/intel/ice/ice.h
> index caaa10157909..ce8b5505b16d 100644
> --- a/drivers/net/ethernet/intel/ice/ice.h
> +++ b/drivers/net/ethernet/intel/ice/ice.h
> @@ -318,6 +318,7 @@ enum ice_vsi_state {
>  	ICE_VSI_UMAC_FLTR_CHANGED,
>  	ICE_VSI_MMAC_FLTR_CHANGED,
>  	ICE_VSI_PROMISC_CHANGED,
> +	ICE_VSI_REBUILD_PENDING,
>  	ICE_VSI_STATE_NBITS		/* must be last */
>  };
>  
> @@ -411,6 +412,7 @@ struct ice_vsi {
>  	struct ice_tx_ring **xdp_rings;	 /* XDP ring array */
>  	u16 num_xdp_txq;		 /* Used XDP queues */
>  	u8 xdp_mapping_mode;		 /* ICE_MAP_MODE_[CONTIG|SCATTER] */
> +	struct mutex xdp_state_lock;
>  
>  	struct net_device **target_netdevs;
>  
> diff --git a/drivers/net/ethernet/intel/ice/ice_lib.c b/drivers/net/ethernet/intel/ice/ice_lib.c
> index 5f2ddcaf7031..a8721ecdf2cd 100644
> --- a/drivers/net/ethernet/intel/ice/ice_lib.c
> +++ b/drivers/net/ethernet/intel/ice/ice_lib.c
> @@ -447,6 +447,7 @@ static void ice_vsi_free(struct ice_vsi *vsi)
>  
>  	ice_vsi_free_stats(vsi);
>  	ice_vsi_free_arrays(vsi);
> +	mutex_destroy(&vsi->xdp_state_lock);
>  	mutex_unlock(&pf->sw_mutex);
>  	devm_kfree(dev, vsi);
>  }
> @@ -626,6 +627,8 @@ static struct ice_vsi *ice_vsi_alloc(struct ice_pf *pf)
>  	pf->next_vsi = ice_get_free_slot(pf->vsi, pf->num_alloc_vsi,
>  					 pf->next_vsi);
>  
> +	mutex_init(&vsi->xdp_state_lock);
> +
>  unlock_pf:
>  	mutex_unlock(&pf->sw_mutex);
>  	return vsi;
> @@ -2973,19 +2976,24 @@ int ice_vsi_rebuild(struct ice_vsi *vsi, u32 vsi_flags)
>  	if (WARN_ON(vsi->type == ICE_VSI_VF && !vsi->vf))
>  		return -EINVAL;
>  
> +	mutex_lock(&vsi->xdp_state_lock);
> +	clear_bit(ICE_VSI_REBUILD_PENDING, vsi->state);

I am not sure what we be the state of interface if rebuild wouldn't
succeed but it feels like clearing this bit should happen at the end of
rebuild when we are sure it was succesful?

> +
>  	ret = ice_vsi_realloc_stat_arrays(vsi);
>  	if (ret)
> -		goto err_vsi_cfg;
> +		goto unlock;
>  
>  	ice_vsi_decfg(vsi);
>  	ret = ice_vsi_cfg_def(vsi);
>  	if (ret)
> -		goto err_vsi_cfg;
> +		goto unlock;
>  
>  	coalesce = kcalloc(vsi->num_q_vectors,
>  			   sizeof(struct ice_coalesce_stored), GFP_KERNEL);
> -	if (!coalesce)
> -		return -ENOMEM;
> +	if (!coalesce) {
> +		ret = -ENOMEM;
> +		goto decfg;
> +	}
>  
>  	prev_num_q_vectors = ice_vsi_rebuild_get_coalesce(vsi, coalesce);
>  
> @@ -2993,22 +3001,22 @@ int ice_vsi_rebuild(struct ice_vsi *vsi, u32 vsi_flags)
>  	if (ret) {
>  		if (vsi_flags & ICE_VSI_FLAG_INIT) {
>  			ret = -EIO;
> -			goto err_vsi_cfg_tc_lan;
> +			goto free_coalesce;
>  		}
>  
> -		kfree(coalesce);
> -		return ice_schedule_reset(pf, ICE_RESET_PFR);
> +		ret = ice_schedule_reset(pf, ICE_RESET_PFR);
> +		goto free_coalesce;
>  	}
>  
>  	ice_vsi_rebuild_set_coalesce(vsi, coalesce, prev_num_q_vectors);
> -	kfree(coalesce);
>  
> -	return 0;
> -
> -err_vsi_cfg_tc_lan:
> -	ice_vsi_decfg(vsi);
> +free_coalesce:
>  	kfree(coalesce);
> -err_vsi_cfg:
> +decfg:
> +	if (ret)
> +		ice_vsi_decfg(vsi);
> +unlock:
> +	mutex_unlock(&vsi->xdp_state_lock);
>  	return ret;
>  }
>  
> diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
> index 2d286a4609a5..e92f43850671 100644
> --- a/drivers/net/ethernet/intel/ice/ice_main.c
> +++ b/drivers/net/ethernet/intel/ice/ice_main.c
> @@ -595,6 +595,7 @@ ice_prepare_for_reset(struct ice_pf *pf, enum ice_reset_req reset_type)
>  	/* clear SW filtering DB */
>  	ice_clear_hw_tbls(hw);
>  	/* disable the VSIs and their queues that are not already DOWN */
> +	set_bit(ICE_VSI_REBUILD_PENDING, ice_get_main_vsi(pf)->state);
>  	ice_pf_dis_all_vsi(pf, false);
>  
>  	if (test_bit(ICE_FLAG_PTP_SUPPORTED, pf->flags))
> @@ -2995,7 +2996,8 @@ ice_xdp_setup_prog(struct ice_vsi *vsi, struct bpf_prog *prog,
>  	}
>  
>  	/* hot swap progs and avoid toggling link */
> -	if (ice_is_xdp_ena_vsi(vsi) == !!prog) {
> +	if (ice_is_xdp_ena_vsi(vsi) == !!prog ||
> +	    test_bit(ICE_VSI_REBUILD_PENDING, vsi->state)) {
>  		ice_vsi_assign_bpf_prog(vsi, prog);
>  		return 0;
>  	}
> @@ -3067,21 +3069,28 @@ static int ice_xdp(struct net_device *dev, struct netdev_bpf *xdp)
>  {
>  	struct ice_netdev_priv *np = netdev_priv(dev);
>  	struct ice_vsi *vsi = np->vsi;
> +	int ret;
>  
>  	if (vsi->type != ICE_VSI_PF) {
>  		NL_SET_ERR_MSG_MOD(xdp->extack, "XDP can be loaded only on PF VSI");
>  		return -EINVAL;
>  	}
>  
> +	mutex_lock(&vsi->xdp_state_lock);
> +
>  	switch (xdp->command) {
>  	case XDP_SETUP_PROG:
> -		return ice_xdp_setup_prog(vsi, xdp->prog, xdp->extack);
> +		ret = ice_xdp_setup_prog(vsi, xdp->prog, xdp->extack);
> +		break;
>  	case XDP_SETUP_XSK_POOL:
> -		return ice_xsk_pool_setup(vsi, xdp->xsk.pool,
> -					  xdp->xsk.queue_id);
> +		ret = ice_xsk_pool_setup(vsi, xdp->xsk.pool, xdp->xsk.queue_id);
> +		break;
>  	default:
> -		return -EINVAL;
> +		ret = -EINVAL;
>  	}
> +
> +	mutex_unlock(&vsi->xdp_state_lock);
> +	return ret;
>  }
>  
>  /**
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 240a7bec242b..a659951fa987 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -390,7 +390,8 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>  		goto failure;
>  	}
>  
> -	if_running = netif_running(vsi->netdev) && ice_is_xdp_ena_vsi(vsi);
> +	if_running = !test_bit(ICE_VSI_DOWN, vsi->state) &&
> +		     ice_is_xdp_ena_vsi(vsi);
>  
>  	if (if_running) {
>  		struct ice_rx_ring *rx_ring = vsi->rx_rings[qid];
> -- 
> 2.43.0
>