[dpdk-dev] [PATCH v4 2/3] lib/lpm: memory orderings to avoid race conditions for v20

[Vladimir Medvedkin]

Hi all,

пт, 5 июл. 2019 г. в 17:52, Medvedkin, Vladimir <
vladimir.medvedkin at intel.com>:

> Hi Wang,
>
> On 03/07/2019 06:44, Ruifeng Wang wrote:
> > When a tbl8 group is getting attached to a tbl24 entry, lookup
> > might fail even though the entry is configured in the table.
> >
> > For ex: consider a LPM table configured with 10.10.10.1/24.
> > When a new entry 10.10.10.32/28 is being added, a new tbl8
> > group is allocated and tbl24 entry is changed to point to
> > the tbl8 group. If the tbl24 entry is written without the tbl8
> > group entries updated, a lookup on 10.10.10.9 will return
> > failure.
> >
> > Correct memory orderings are required to ensure that the
> > store to tbl24 does not happen before the stores to tbl8 group
> > entries complete.
> >
> > Besides, explicit structure alignment is used to address atomic
> > operation building issue with older version clang.
> >
> > Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
> > Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
> > Reviewed-by: Gavin Hu <gavin.hu at arm.com>
> > ---
> > v4: changed alignment attribute parameter
> > v3: no changes
> > v2: fixed clang building issue by supplying alignment attribute.
> >
> >   lib/librte_lpm/rte_lpm.c | 32 +++++++++++++++++++++++++-------
> >   lib/librte_lpm/rte_lpm.h |  4 ++--
> >   2 files changed, 27 insertions(+), 9 deletions(-)
> >
> > diff --git a/lib/librte_lpm/rte_lpm.c b/lib/librte_lpm/rte_lpm.c
> > index 6ec450a08..baa6e7460 100644
> > --- a/lib/librte_lpm/rte_lpm.c
> > +++ b/lib/librte_lpm/rte_lpm.c
> > @@ -737,7 +737,8 @@ add_depth_small_v20(struct rte_lpm_v20 *lpm,
> uint32_t ip, uint8_t depth,
> >                       /* Setting tbl24 entry in one go to avoid race
> >                        * conditions
> >                        */
> > -                     lpm->tbl24[i] = new_tbl24_entry;
> > +                     __atomic_store(&lpm->tbl24[i], &new_tbl24_entry,
> > +                                     __ATOMIC_RELEASE);
> >
> >                       continue;
> >               }
> > @@ -892,7 +893,8 @@ add_depth_big_v20(struct rte_lpm_v20 *lpm, uint32_t
> ip_masked, uint8_t depth,
> >                       .depth = 0,
> >               };
> >
> > -             lpm->tbl24[tbl24_index] = new_tbl24_entry;
> > +             __atomic_store(&lpm->tbl24[tbl24_index], &new_tbl24_entry,
> > +                             __ATOMIC_RELEASE);
> >
> >       } /* If valid entry but not extended calculate the index into
> Table8. */
> >       else if (lpm->tbl24[tbl24_index].valid_group == 0) {
> > @@ -938,7 +940,8 @@ add_depth_big_v20(struct rte_lpm_v20 *lpm, uint32_t
> ip_masked, uint8_t depth,
> >                               .depth = 0,
> >               };
> >
> > -             lpm->tbl24[tbl24_index] = new_tbl24_entry;
> > +             __atomic_store(&lpm->tbl24[tbl24_index], &new_tbl24_entry,
> > +                             __ATOMIC_RELEASE);
> >
> >       } else { /*
> >               * If it is valid, extended entry calculate the index into
> tbl8.
> > @@ -1320,7 +1323,15 @@ delete_depth_small_v20(struct rte_lpm_v20 *lpm,
> uint32_t ip_masked,
> >
> >                       if (lpm->tbl24[i].valid_group == 0 &&
> >                                       lpm->tbl24[i].depth <= depth) {
> > -                             lpm->tbl24[i].valid = INVALID;
> > +                             struct rte_lpm_tbl_entry_v20
> > +                                     zero_tbl24_entry = {
> > +                                             .valid = INVALID,
> > +                                             .depth = 0,
> > +                                             .valid_group = 0,
> > +                                     };
> > +                                     zero_tbl24_entry.next_hop = 0;
> Why don't you use just "struct rte_lpm_tbl_entry_v20 zero_tbl24_entry =
> {0} " like you do for _v1604?
>
Ah, sorry, just found what you mentioned earlier, this will cause meson
build to fail.

> > +                             __atomic_store(&lpm->tbl24[i],
> > +                                     &zero_tbl24_entry,
> __ATOMIC_RELEASE);
> >                       } else if (lpm->tbl24[i].valid_group == 1) {
> >                               /*
> >                                * If TBL24 entry is extended, then there
> has
> > @@ -1365,7 +1376,8 @@ delete_depth_small_v20(struct rte_lpm_v20 *lpm,
> uint32_t ip_masked,
> >
> >                       if (lpm->tbl24[i].valid_group == 0 &&
> >                                       lpm->tbl24[i].depth <= depth) {
> > -                             lpm->tbl24[i] = new_tbl24_entry;
> > +                             __atomic_store(&lpm->tbl24[i],
> &new_tbl24_entry,
> > +                                             __ATOMIC_RELEASE);
> >                       } else  if (lpm->tbl24[i].valid_group == 1) {
> >                               /*
> >                                * If TBL24 entry is extended, then there
> has
> > @@ -1647,8 +1659,11 @@ delete_depth_big_v20(struct rte_lpm_v20 *lpm,
> uint32_t ip_masked,
> >       tbl8_recycle_index = tbl8_recycle_check_v20(lpm->tbl8,
> tbl8_group_start);
> >
> >       if (tbl8_recycle_index == -EINVAL) {
> > -             /* Set tbl24 before freeing tbl8 to avoid race condition.
> */
> > +             /* Set tbl24 before freeing tbl8 to avoid race condition.
> > +              * Prevent the free of the tbl8 group from hoisting.
> > +              */
> >               lpm->tbl24[tbl24_index].valid = 0;
> > +             __atomic_thread_fence(__ATOMIC_RELEASE);
> >               tbl8_free_v20(lpm->tbl8, tbl8_group_start);
> >       } else if (tbl8_recycle_index > -1) {
> >               /* Update tbl24 entry. */
> > @@ -1659,8 +1674,11 @@ delete_depth_big_v20(struct rte_lpm_v20 *lpm,
> uint32_t ip_masked,
> >                       .depth = lpm->tbl8[tbl8_recycle_index].depth,
> >               };
> >
> > -             /* Set tbl24 before freeing tbl8 to avoid race condition.
> */
> > +             /* 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_thread_fence(__ATOMIC_RELEASE);
> >               tbl8_free_v20(lpm->tbl8, tbl8_group_start);
> >       }
> >
> > diff --git a/lib/librte_lpm/rte_lpm.h b/lib/librte_lpm/rte_lpm.h
> > index 6f5704c5c..906ec4483 100644
> > --- a/lib/librte_lpm/rte_lpm.h
> > +++ b/lib/librte_lpm/rte_lpm.h
> > @@ -88,7 +88,7 @@ struct rte_lpm_tbl_entry_v20 {
> >        */
> >       uint8_t valid_group :1;
> >       uint8_t depth       :6; /**< Rule depth. */
> > -};
> > +} __rte_aligned(sizeof(uint16_t));
> >
> >   __extension__
> >   struct rte_lpm_tbl_entry {
> > @@ -121,7 +121,7 @@ struct rte_lpm_tbl_entry_v20 {
> >               uint8_t group_idx;
> >               uint8_t next_hop;
> >       };
> > -};
> > +} __rte_aligned(sizeof(uint16_t));
> >
> >   __extension__
> >   struct rte_lpm_tbl_entry {
>
> --
> Regards,
> Vladimir
>
>

-- 
Regards,
Vladimir