Re: [dpdk-stable] [dpdk-dev] [PATCH v4] mbuf: fix reset on mbuf free

["Morten Brørup" <mb@smartsharesystems.com>]

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Olivier Matz
> Sent: Wednesday, 13 January 2021 14.28

[snip]

> Fixes: 8f094a9ac5d7 ("mbuf: set mbuf fields while in pool")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
> Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> ---
> 
> v4
> * add a unit test (suggested by David)
> 
> v3
> * fix commit log again (thanks Morten for spotting it)
> 
> v2
> * avoid write access if uneeded (suggested by Konstantin)
> * enhance comments in mbuf header file (suggested by Morten)
> * fix commit log
> 
>  app/test/test_mbuf.c            | 69 +++++++++++++++++++++++++++++++++
>  lib/librte_mbuf/rte_mbuf.c      |  4 +-
>  lib/librte_mbuf/rte_mbuf.h      |  8 ++--
>  lib/librte_mbuf/rte_mbuf_core.h | 13 ++++++-
>  4 files changed, 86 insertions(+), 8 deletions(-)
> 

[snip]

> diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
> index 7d09ee2939..5f77840557 100644
> --- a/lib/librte_mbuf/rte_mbuf.c
> +++ b/lib/librte_mbuf/rte_mbuf.c
> @@ -129,10 +129,10 @@ rte_pktmbuf_free_pinned_extmem(void *addr, void
> *opaque)
> 
>  	rte_mbuf_ext_refcnt_set(m->shinfo, 1);
>  	m->ol_flags = EXT_ATTACHED_MBUF;
> -	if (m->next != NULL) {
> +	if (m->next != NULL)
>  		m->next = NULL;
> +	if (m->nb_segs != 1)
>  		m->nb_segs = 1;
> -	}
>  	rte_mbuf_raw_free(m);
>  }
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index c4c9ebfaa0..8c1097ed76 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -1340,10 +1340,10 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>  				return NULL;
>  		}
> 
> -		if (m->next != NULL) {
> +		if (m->next != NULL)
>  			m->next = NULL;
> +		if (m->nb_segs != 1)
>  			m->nb_segs = 1;
> -		}
> 
>  		return m;
> 
> @@ -1357,10 +1357,10 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>  				return NULL;
>  		}
> 
> -		if (m->next != NULL) {
> +		if (m->next != NULL)
>  			m->next = NULL;
> +		if (m->nb_segs != 1)
>  			m->nb_segs = 1;
> -		}
>  		rte_mbuf_refcnt_set(m, 1);
> 
>  		return m;

Olivier, have you considered if Konstantin's suggestion (to avoid write access if unneeded) could be applied to any of the other functions in rte_mbuf.h, e.g. __rte_pktmbuf_free_direct()?