Subject: Re: [PATCH v2] ice: fix race condition in TX timestamp ring cleanup

From: Maciej Fijalkowski <[email-masked]>
Date: Thu, 5 Feb 2026 14:43:11 +0100

On Thu, Feb 05, 2026 at 11:43:27AM +0900, Keita Morisaki wrote:
> Fix a race condition between ice_free_tx_tstamp_ring() and ice_tx_map()
> that can cause a NULL pointer dereference.
> 
> ice_free_tx_tstamp_ring currently clears the ICE_TX_FLAGS_TXTIME flag
> after NULLing the tstamp_ring. This could allow a concurrent ice_tx_map
> call on another CPU to dereference the tstamp_ring, which could lead to
> a NULL pointer dereference.
> 
>   CPU A:ice_free_tx_tstamp_ring() | CPU B:ice_tx_map()
>   --------------------------------|---------------------------------
>   tx_ring->tstamp_ring = NULL     |
>                                   | ice_is_txtime_cfg() -> true
>                                   | tstamp_ring = tx_ring->tstamp_ring
>                                   | tstamp_ring->count  // NULL deref!
>   flags &= ~ICE_TX_FLAGS_TXTIME   |
> 
> Fix by:
> 1. Reordering ice_free_tx_tstamp_ring() to clear the flag before
>    NULLing the pointer, with smp_wmb() to ensure proper ordering.
> 2. Adding smp_rmb() in ice_tx_map() after the flag check to order the
>    flag read before the pointer read, using READ_ONCE() for the
>    pointer, and adding a NULL check as a safety net.
> 3. Converting tx_ring->flags from u8 to DECLARE_BITMAP() and using
>    atomic bitops (set_bit(), clear_bit(), test_bit()) for all flag
>    operations throughout the driver:
>    - ICE_TX_RING_FLAGS_XDP
>    - ICE_TX_RING_FLAGS_VLAN_L2TAG1
>    - ICE_TX_RING_FLAGS_VLAN_L2TAG2
>    - ICE_TX_RING_FLAGS_TXTIME

Hi Keita,

am I reading this right or you only modified flags to be bitmap on Tx side
and Rx is left as-is?

Would be nice to reflect this on Rx side as well, but I know it is out of
the scope for this patch.

Would you like to do a follow-up patch for that which would be sent to
-next tree?

Also your patch should contain the tree you are dedicating your work:
[PATCH net v2] ice: fix race condition in TX timestamp ring cleanup

As for rest of the stuff it makes sense to me, however best if Paul could
give his ack here.

> 
> Fixes: ccde82e909467 ("ice: add E830 Earliest TxTime First Offload support")
> Signed-off-by: Keita Morisaki <[email-masked]>
> Reviewed-by: Aleksandr Loktionov <[email-masked]>
> ---
> Changes in v2:
> - Convert tx_ring->flags from u8 to DECLARE_BITMAP() and use atomic
>   bitops (set_bit(), clear_bit(), test_bit()) for all flag operations
>   instead of WRITE_ONCE() for flag updates
> - Rename flags from ICE_TX_FLAGS_RING_* to ICE_TX_RING_FLAGS_* to
>   distinguish from per-packet flags (ICE_TX_FLAGS_*)
> 
>  drivers/net/ethernet/intel/ice/ice.h         |  4 ++--
>  drivers/net/ethernet/intel/ice/ice_dcb_lib.c |  2 +-
>  drivers/net/ethernet/intel/ice/ice_lib.c     |  4 ++--
>  drivers/net/ethernet/intel/ice/ice_txrx.c    | 23 ++++++++++++++------
>  drivers/net/ethernet/intel/ice/ice_txrx.h    | 16 +++++++++-----
>  5 files changed, 31 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice.h b/drivers/net/ethernet/intel/ice/ice.h
> index 00f75d87c73f9..5baeca824cd99 100644
> --- a/drivers/net/ethernet/intel/ice/ice.h
> +++ b/drivers/net/ethernet/intel/ice/ice.h
> @@ -753,7 +753,7 @@ static inline bool ice_is_xdp_ena_vsi(struct ice_vsi *vsi)
>  
>  static inline void ice_set_ring_xdp(struct ice_tx_ring *ring)
>  {
> -	ring->flags |= ICE_TX_FLAGS_RING_XDP;
> +	set_bit(ICE_TX_RING_FLAGS_XDP, ring->flags);
>  }
>  
>  /**
> @@ -778,7 +778,7 @@ static inline bool ice_is_txtime_ena(const struct ice_tx_ring *ring)
>   */
>  static inline bool ice_is_txtime_cfg(const struct ice_tx_ring *ring)
>  {
> -	return !!(ring->flags & ICE_TX_FLAGS_TXTIME);
> +	return test_bit(ICE_TX_RING_FLAGS_TXTIME, ring->flags);
>  }
>  
>  /**
> diff --git a/drivers/net/ethernet/intel/ice/ice_dcb_lib.c b/drivers/net/ethernet/intel/ice/ice_dcb_lib.c
> index 9fc8681cc58ea..bd74344271f3f 100644
> --- a/drivers/net/ethernet/intel/ice/ice_dcb_lib.c
> +++ b/drivers/net/ethernet/intel/ice/ice_dcb_lib.c
> @@ -943,7 +943,7 @@ ice_tx_prepare_vlan_flags_dcb(struct ice_tx_ring *tx_ring,
>  		/* if this is not already set it means a VLAN 0 + priority needs
>  		 * to be offloaded
>  		 */
> -		if (tx_ring->flags & ICE_TX_FLAGS_RING_VLAN_L2TAG2)
> +		if (test_bit(ICE_TX_RING_FLAGS_VLAN_L2TAG2, tx_ring->flags))
>  			first->tx_flags |= ICE_TX_FLAGS_HW_OUTER_SINGLE_VLAN;
>  		else
>  			first->tx_flags |= ICE_TX_FLAGS_HW_VLAN;
> diff --git a/drivers/net/ethernet/intel/ice/ice_lib.c b/drivers/net/ethernet/intel/ice/ice_lib.c
> index d47af94f31a99..55ff0708d136e 100644
> --- a/drivers/net/ethernet/intel/ice/ice_lib.c
> +++ b/drivers/net/ethernet/intel/ice/ice_lib.c
> @@ -1412,9 +1412,9 @@ static int ice_vsi_alloc_rings(struct ice_vsi *vsi)
>  		ring->count = vsi->num_tx_desc;
>  		ring->txq_teid = ICE_INVAL_TEID;
>  		if (dvm_ena)
> -			ring->flags |= ICE_TX_FLAGS_RING_VLAN_L2TAG2;
> +			set_bit(ICE_TX_RING_FLAGS_VLAN_L2TAG2, ring->flags);
>  		else
> -			ring->flags |= ICE_TX_FLAGS_RING_VLAN_L2TAG1;
> +			set_bit(ICE_TX_RING_FLAGS_VLAN_L2TAG1, ring->flags);
>  		WRITE_ONCE(vsi->tx_rings[i], ring);
>  	}
>  
> diff --git a/drivers/net/ethernet/intel/ice/ice_txrx.c b/drivers/net/ethernet/intel/ice/ice_txrx.c
> index ad76768a42323..564e4e33ecbc3 100644
> --- a/drivers/net/ethernet/intel/ice/ice_txrx.c
> +++ b/drivers/net/ethernet/intel/ice/ice_txrx.c
> @@ -190,9 +190,10 @@ void ice_free_tstamp_ring(struct ice_tx_ring *tx_ring)
>  void ice_free_tx_tstamp_ring(struct ice_tx_ring *tx_ring)
>  {
>  	ice_free_tstamp_ring(tx_ring);
> +	clear_bit(ICE_TX_RING_FLAGS_TXTIME, tx_ring->flags);
> +	smp_wmb();	/* order flag clear before pointer NULL */
>  	kfree_rcu(tx_ring->tstamp_ring, rcu);
> -	tx_ring->tstamp_ring = NULL;
> -	tx_ring->flags &= ~ICE_TX_FLAGS_TXTIME;
> +	WRITE_ONCE(tx_ring->tstamp_ring, NULL);
>  }
>  
>  /**
> @@ -405,7 +406,7 @@ static int ice_alloc_tstamp_ring(struct ice_tx_ring *tx_ring)
>  	tx_ring->tstamp_ring = tstamp_ring;
>  	tstamp_ring->desc = NULL;
>  	tstamp_ring->count = ice_calc_ts_ring_count(tx_ring);
> -	tx_ring->flags |= ICE_TX_FLAGS_TXTIME;
> +	set_bit(ICE_TX_RING_FLAGS_TXTIME, tx_ring->flags);
>  	return 0;
>  }
>  
> @@ -1519,13 +1520,20 @@ ice_tx_map(struct ice_tx_ring *tx_ring, struct ice_tx_buf *first,
>  		return;
>  
>  	if (ice_is_txtime_cfg(tx_ring)) {
> -		struct ice_tstamp_ring *tstamp_ring = tx_ring->tstamp_ring;
> -		u32 tstamp_count = tstamp_ring->count;
> -		u32 j = tstamp_ring->next_to_use;
> +		struct ice_tstamp_ring *tstamp_ring;
> +		u32 tstamp_count, j;
>  		struct ice_ts_desc *ts_desc;
>  		struct timespec64 ts;
>  		u32 tstamp;
>  
> +		smp_rmb();	/* order flag read before pointer read */
> +		tstamp_ring = READ_ONCE(tx_ring->tstamp_ring);
> +		if (unlikely(!tstamp_ring))
> +			goto ring_kick;
> +
> +		tstamp_count = tstamp_ring->count;
> +		j = tstamp_ring->next_to_use;
> +
>  		ts = ktime_to_timespec64(first->skb->tstamp);
>  		tstamp = ts.tv_nsec >> ICE_TXTIME_CTX_RESOLUTION_128NS;
>  
> @@ -1553,6 +1561,7 @@ ice_tx_map(struct ice_tx_ring *tx_ring, struct ice_tx_buf *first,
>  		tstamp_ring->next_to_use = j;
>  		writel_relaxed(j, tstamp_ring->tail);
>  	} else {
> +ring_kick:
>  		writel_relaxed(i, tx_ring->tail);
>  	}
>  	return;
> @@ -1812,7 +1821,7 @@ ice_tx_prepare_vlan_flags(struct ice_tx_ring *tx_ring, struct ice_tx_buf *first)
>  	 */
>  	if (skb_vlan_tag_present(skb)) {
>  		first->vid = skb_vlan_tag_get(skb);
> -		if (tx_ring->flags & ICE_TX_FLAGS_RING_VLAN_L2TAG2)
> +		if (test_bit(ICE_TX_RING_FLAGS_VLAN_L2TAG2, tx_ring->flags))
>  			first->tx_flags |= ICE_TX_FLAGS_HW_OUTER_SINGLE_VLAN;
>  		else
>  			first->tx_flags |= ICE_TX_FLAGS_HW_VLAN;
> diff --git a/drivers/net/ethernet/intel/ice/ice_txrx.h b/drivers/net/ethernet/intel/ice/ice_txrx.h
> index e440c55d9e9f0..d35ffdc3dc84d 100644
> --- a/drivers/net/ethernet/intel/ice/ice_txrx.h
> +++ b/drivers/net/ethernet/intel/ice/ice_txrx.h
> @@ -181,6 +181,14 @@ enum ice_rx_dtype {
>  	ICE_RX_DTYPE_SPLIT_ALWAYS	= 2,
>  };
>  
> +enum ice_tx_ring_flags {
> +	ICE_TX_RING_FLAGS_XDP,
> +	ICE_TX_RING_FLAGS_VLAN_L2TAG1,
> +	ICE_TX_RING_FLAGS_VLAN_L2TAG2,
> +	ICE_TX_RING_FLAGS_TXTIME,
> +	ICE_TX_RING_FLAGS_NBITS,
> +};
> +
>  struct ice_pkt_ctx {
>  	u64 cached_phctime;
>  	__be16 vlan_proto;
> @@ -333,11 +341,7 @@ struct ice_tx_ring {
>  	u32 txq_teid;			/* Added Tx queue TEID */
>  	/* CL4 - 4th cacheline starts here */
>  	struct ice_tstamp_ring *tstamp_ring;
> -#define ICE_TX_FLAGS_RING_XDP		BIT(0)
> -#define ICE_TX_FLAGS_RING_VLAN_L2TAG1	BIT(1)
> -#define ICE_TX_FLAGS_RING_VLAN_L2TAG2	BIT(2)
> -#define ICE_TX_FLAGS_TXTIME		BIT(3)
> -	u8 flags;
> +	DECLARE_BITMAP(flags, ICE_TX_RING_FLAGS_NBITS);
>  	u8 dcb_tc;			/* Traffic class of ring */
>  	u16 quanta_prof_id;
>  } ____cacheline_internodealigned_in_smp;
> @@ -349,7 +353,7 @@ static inline bool ice_ring_ch_enabled(struct ice_tx_ring *ring)
>  
>  static inline bool ice_ring_is_xdp(struct ice_tx_ring *ring)
>  {
> -	return !!(ring->flags & ICE_TX_FLAGS_RING_XDP);
> +	return test_bit(ICE_TX_RING_FLAGS_XDP, ring->flags);
>  }
>  
>  enum ice_container_type {
> 
> base-commit: 18f7fcd5e69a04df57b563360b88be72471d6b62
> -- 
> 2.34.1
>