Re: [dpdk-dev] [PATCH v3] mbuf: fix dynamic flags lookup from secondary process

[Olivier Matz]

Hi Stephen,

On Fri, Oct 23, 2020 at 05:43:31PM -0700, Stephen Hemminger wrote:
> The dynamic flag management is broken if rte_mbuf_dynflag_lookup()
> is done in a secondary process because the local pointer to
> the memzone is not ever initialized.
> 
> Fix it by using the same checks as dynfield_register().
> I.e if shared memory zone has not been looked up already,
> then discover it.
> 
> Fixes: 4958ca3a443a ("mbuf: support dynamic fields and flags")
> Cc: olivier.m...@6wind.com
> Signed-off-by: Stephen Hemminger <step...@networkplumber.org>
> ---
> 
> v3 - change title, fix one extra whitespace 
> 
>  lib/librte_mbuf/rte_mbuf_dyn.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf_dyn.c b/lib/librte_mbuf/rte_mbuf_dyn.c
> index 538a43f6959f..554ec5a1ca4f 100644
> --- a/lib/librte_mbuf/rte_mbuf_dyn.c
> +++ b/lib/librte_mbuf/rte_mbuf_dyn.c
> @@ -185,13 +185,11 @@ rte_mbuf_dynfield_lookup(const char *name, struct 
> rte_mbuf_dynfield *params)
>  {
>       struct mbuf_dynfield_elt *mbuf_dynfield;
>  
> -     if (shm == NULL) {
> -             rte_errno = ENOENT;
> -             return -1;
> -     }
> -
>       rte_mcfg_tailq_read_lock();
> -     mbuf_dynfield = __mbuf_dynfield_lookup(name);
> +     if (shm == NULL && init_shared_mem() < 0)
> +             mbuf_dynfield = NULL;
> +     else
> +             mbuf_dynfield = __mbuf_dynfield_lookup(name);
>       rte_mcfg_tailq_read_unlock();
>  
>       if (mbuf_dynfield == NULL) {
>               rte_errno = ENOENT;
>               return -1;

There is still a small corner case here: on a primary process,
init_shared_mem() can return -1 in case rte_memzone_reserve_aligned()
returns a NULL memzone. In this situation, rte_errno is set by the
memzone layer by overriden to ENOENT.

Maybe something like this is better, what do you think?

@@ -172,7 +172,7 @@ __mbuf_dynfield_lookup(const char *name)
                        break;
        }
 
-       if (te == NULL) {
+       if (te == NULL || mbuf_dynfield == NULL) {
                rte_errno = ENOENT;
                return NULL;
        }
@@ -185,19 +185,15 @@ rte_mbuf_dynfield_lookup(const char *name, struct 
rte_mbuf_dynfield *params)
 {
        struct mbuf_dynfield_elt *mbuf_dynfield;
 
-       if (shm == NULL) {
-               rte_errno = ENOENT;
-               return -1;
-       }
-
        rte_mcfg_tailq_read_lock();
-       mbuf_dynfield = __mbuf_dynfield_lookup(name);
+       if (shm == NULL && init_shared_mem() < 0)
+               mbuf_dynfield = NULL;
+       else
+               mbuf_dynfield = __mbuf_dynfield_lookup(name);
        rte_mcfg_tailq_read_unlock();
 
-       if (mbuf_dynfield == NULL) {
-               rte_errno = ENOENT;
+       if (mbuf_dynfield == NULL)
                return -1;
-       }
 
        if (params != NULL)
                memcpy(params, &mbuf_dynfield->params, sizeof(*params));



Thanks,
Olivier


> @@ -384,13 +382,11 @@ rte_mbuf_dynflag_lookup(const char *name,
>  {
>       struct mbuf_dynflag_elt *mbuf_dynflag;
>  
> -     if (shm == NULL) {
> -             rte_errno = ENOENT;
> -             return -1;
> -     }
> -
>       rte_mcfg_tailq_read_lock();
> -     mbuf_dynflag = __mbuf_dynflag_lookup(name);
> +     if (shm == NULL && init_shared_mem() < 0)
> +             mbuf_dynflag = NULL;
> +     else
> +             mbuf_dynflag = __mbuf_dynflag_lookup(name);
>       rte_mcfg_tailq_read_unlock();
>  
>       if (mbuf_dynflag == NULL) {
> -- 
> 2.27.0
>