[dpdk-dev] [PATCH v4 3/3] lib/lpm: use atomic store to avoid partial update

[Medvedkin, Vladimir]

Hi Wang,

On 03/07/2019 06:44, Ruifeng Wang wrote:
> Compiler could generate non-atomic stores for whole table entry
> updating. This may cause incorrect nexthop to be returned, if
> the byte with valid flag is updated prior to the byte with next
> hot is updated.
>
> Changed to use atomic store to update whole table entry.
>
> Suggested-by: Medvedkin Vladimir <vladimir.medvedkin at intel.com>
> Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
> Reviewed-by: Gavin Hu <gavin.hu at arm.com>
> ---
> v4: initial version
>
>   lib/librte_lpm/rte_lpm.c | 34 ++++++++++++++++++++++++----------
>   1 file changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/lib/librte_lpm/rte_lpm.c b/lib/librte_lpm/rte_lpm.c
> index baa6e7460..5d1dbd7e6 100644
> --- a/lib/librte_lpm/rte_lpm.c
> +++ b/lib/librte_lpm/rte_lpm.c
> @@ -767,7 +767,9 @@ add_depth_small_v20(struct rte_lpm_v20 *lpm, uint32_t ip, uint8_t depth,
>   					 * Setting tbl8 entry in one go to avoid
>   					 * race conditions
>   					 */
> -					lpm->tbl8[j] = new_tbl8_entry;
> +					__atomic_store(&lpm->tbl8[j],
> +						&new_tbl8_entry,
> +						__ATOMIC_RELAXED);
>   
>   					continue;
>   				}
> @@ -837,7 +839,9 @@ add_depth_small_v1604(struct rte_lpm *lpm, uint32_t ip, uint8_t depth,
>   					 * Setting tbl8 entry in one go to avoid
>   					 * race conditions
>   					 */
> -					lpm->tbl8[j] = new_tbl8_entry;
> +					__atomic_store(&lpm->tbl8[j],
> +						&new_tbl8_entry,
> +						__ATOMIC_RELAXED);
>   
>   					continue;
>   				}
> @@ -965,7 +969,8 @@ add_depth_big_v20(struct rte_lpm_v20 *lpm, uint32_t ip_masked, uint8_t depth,
>   				 * Setting tbl8 entry in one go to avoid race
>   				 * condition
>   				 */
> -				lpm->tbl8[i] = new_tbl8_entry;
> +				__atomic_store(&lpm->tbl8[i], &new_tbl8_entry,
> +						__ATOMIC_RELAXED);
>   
>   				continue;
>   			}
> @@ -1100,7 +1105,8 @@ add_depth_big_v1604(struct rte_lpm *lpm, uint32_t ip_masked, uint8_t depth,
>   				 * Setting tbl8 entry in one go to avoid race
>   				 * condition
>   				 */
> -				lpm->tbl8[i] = new_tbl8_entry;
> +				__atomic_store(&lpm->tbl8[i], &new_tbl8_entry,
> +						__ATOMIC_RELAXED);
>   
>   				continue;
>   			}
> @@ -1393,7 +1399,9 @@ delete_depth_small_v20(struct rte_lpm_v20 *lpm, uint32_t ip_masked,
>   					RTE_LPM_TBL8_GROUP_NUM_ENTRIES); j++) {
>   
>   					if (lpm->tbl8[j].depth <= depth)
> -						lpm->tbl8[j] = new_tbl8_entry;
> +						__atomic_store(&lpm->tbl8[j],
> +							&new_tbl8_entry,
> +							__ATOMIC_RELAXED);
>   				}
>   			}
>   		}
> @@ -1490,7 +1498,9 @@ delete_depth_small_v1604(struct rte_lpm *lpm, uint32_t ip_masked,
>   					RTE_LPM_TBL8_GROUP_NUM_ENTRIES); j++) {
>   
>   					if (lpm->tbl8[j].depth <= depth)
> -						lpm->tbl8[j] = new_tbl8_entry;
> +						__atomic_store(&lpm->tbl8[j],
> +							&new_tbl8_entry,
> +							__ATOMIC_RELAXED);
>   				}
>   			}
>   		}
> @@ -1646,7 +1656,8 @@ delete_depth_big_v20(struct rte_lpm_v20 *lpm, uint32_t ip_masked,
>   		 */
>   		for (i = tbl8_index; i < (tbl8_index + tbl8_range); i++) {
>   			if (lpm->tbl8[i].depth <= depth)
> -				lpm->tbl8[i] = new_tbl8_entry;
> +				__atomic_store(&lpm->tbl8[i], &new_tbl8_entry,
> +						__ATOMIC_RELAXED);
>   		}
>   	}
>   
> @@ -1677,7 +1688,8 @@ delete_depth_big_v20(struct rte_lpm_v20 *lpm, uint32_t ip_masked,
>   		/* Set tbl24 before freeing tbl8 to avoid race condition.
>   		 * Prevent the free of the tbl8 group from hoisting.
>   		 */
> -		lpm->tbl24[tbl24_index] = new_tbl24_entry;
> +		__atomic_store(&lpm->tbl24[tbl24_index], &new_tbl24_entry,
> +				__ATOMIC_RELAXED);
>   		__atomic_thread_fence(__ATOMIC_RELEASE);
>   		tbl8_free_v20(lpm->tbl8, tbl8_group_start);
>   	}
> @@ -1730,7 +1742,8 @@ delete_depth_big_v1604(struct rte_lpm *lpm, uint32_t ip_masked,
>   		 */
>   		for (i = tbl8_index; i < (tbl8_index + tbl8_range); i++) {
>   			if (lpm->tbl8[i].depth <= depth)
> -				lpm->tbl8[i] = new_tbl8_entry;
> +				__atomic_store(&lpm->tbl8[i], &new_tbl8_entry,
> +						__ATOMIC_RELAXED);
>   		}
>   	}
>   
> @@ -1761,7 +1774,8 @@ delete_depth_big_v1604(struct rte_lpm *lpm, uint32_t ip_masked,
>   		/* Set tbl24 before freeing tbl8 to avoid race condition.
>   		 * Prevent the free of the tbl8 group from hoisting.
>   		 */
> -		lpm->tbl24[tbl24_index] = new_tbl24_entry;
> +		__atomic_store(&lpm->tbl24[tbl24_index], &new_tbl24_entry,
> +				__ATOMIC_RELAXED);
>   		__atomic_thread_fence(__ATOMIC_RELEASE);
Do you really need __atomic_thread_fence after atomic_store?
>   		tbl8_free_v1604(lpm->tbl8, tbl8_group_start);
>   	}

-- 
Regards,
Vladimir