<snip>
> > > >
> > > > >
> > > > > Hi Phil,
> > > > >
> > > > > Good catch - thanks for the fix. I've commented in-line:
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Phil Yang <phil.y...@arm.com>
> > > > > > Sent: Friday, June 12, 2020 6:20 AM
> > > > > > To: dev@dpdk.org; Carrillo, Erik G <erik.g.carri...@intel.com>
> > > > > > Cc: d...@linux.vnet.ibm.com; honnappa.nagaraha...@arm.com;
> > > > > > ruifeng.w...@arm.com; dharmik.thak...@arm.com; n...@arm.com;
> > > > > > sta...@dpdk.org
> > > > > > Subject: [PATCH 1/3] eventdev: fix race condition on timer
> > > > > > list counter
> > > > > >
> > > > > > The n_poll_lcores counter and poll_lcore array are shared
> > > > > > between lcores and the update of these variables are out of
> > > > > > the protection of spinlock on each lcore timer list. The
> > > > > > read-modify-write operations of the counter are not atomic, so
> > > > > > it has the potential of race condition
> > > > > between lcores.
> > > > > >
> > > > > > Use c11 atomics with RELAXED ordering to prevent confliction.
> > > > > >
> > > > > > Fixes: cc7b73ea9e3b ("eventdev: add new software timer
> > > > > > adapter")
> > > > > > Cc: erik.g.carri...@intel.com
> > > > > > Cc: sta...@dpdk.org
> > > > > >
> > > > > > Signed-off-by: Phil Yang <phil.y...@arm.com>
> > > > > > Reviewed-by: Dharmik Thakkar <dharmik.thak...@arm.com>
> > > > > > Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
> > > > > > ---
> > > > > > lib/librte_eventdev/rte_event_timer_adapter.c | 16
> > > > > > ++++++++++++----
> > > > > > 1 file changed, 12 insertions(+), 4 deletions(-)
> > > > > >
> > > > > > diff --git a/lib/librte_eventdev/rte_event_timer_adapter.c
> > > > > > b/lib/librte_eventdev/rte_event_timer_adapter.c
> > > > > > index 005459f..6a0e283 100644
> > > > > > --- a/lib/librte_eventdev/rte_event_timer_adapter.c
> > > > > > +++ b/lib/librte_eventdev/rte_event_timer_adapter.c
> > > > > > @@ -583,6 +583,7 @@ swtim_callback(struct rte_timer *tim)
> > > > > > uint16_t nb_evs_invalid = 0; uint64_t opaque; int ret;
> > > > > > +int n_lcores;
> > > > > >
> > > > > > opaque = evtim->impl_opaque[1]; adapter = (struct
> > > > > > rte_event_timer_adapter *)(uintptr_t)opaque; @@
> > > > > > -605,8 +606,12 @@ swtim_callback(struct rte_timer *tim)
> > > > > > "with immediate expiry value"); }
> > > > > >
> > > > > > -if (unlikely(rte_atomic16_test_and_set(&sw-
> > > > > > >in_use[lcore].v)))
> > > > > > -sw->poll_lcores[sw->n_poll_lcores++] = lcore;
> > > > > > +if (unlikely(rte_atomic16_test_and_set(&sw-
> > > > > > >in_use[lcore].v))) {
> > > > > > +n_lcores = __atomic_fetch_add(&sw->n_poll_lcores,
> > > > > > 1,
> > > > > > +__ATOMIC_RELAXED);
> > > > Since this commit will be back ported, we should prefer to use
> > > > rte_atomic APIs for this commit. Otherwise, we will have a mix of
> > > > rte_atomic and C11 APIs.
> > > > My suggestion is to fix this bug using rte_atomic so that
> > > > backported code will have only rte_atomic APIs. Add another commit
> > > > (if
> > > > required) in this series to make the bug fix use C11 APIs (this
> > > > commit will not be
> > > backported).
> > >
> > > Hi Honnappa,
> > >
> > > It doesn't have an applicable rte_atomic_XXX API to fix this issue.
> > > The rte_atomic32_inc doesn't return the original value of the input
> > > parameter and rte_atomic32_add_return can only return the new value.
> > Ok, understood.
> >
> > >
> > > Meanwhile, the rte_timer_alt_manage & rte_timer_stop_all API not
> > > support rte_atomic type parameters. We might need to rewrite these
> > > two APIs if we want to use rte_atomic operations for n_pol_lcores
> > > and
> > poll_lcores array.
> > >
> > > So, a better solution could be to backport the entire c11 solution
> > > to stable releases.
> > I am ok with the approach.
> > Erik, are you ok with this?
> >
>
> Yes, I'm OK with that as well.
Thanks Erik. I think we need to add sta...@dpdk.org to Cc for all the commits
in the series.
>
> Thanks,
> Erik
>
> > >
> > > Thanks,
> > > Phil
> > >
> > > >
> > > > >
> > > > > Just a nit, but let's align the continued line with the opening
> > > > > parentheses in this location and below. With these changes:
> > > > >
> > > > > Acked-by: Erik Gabriel Carrillo <erik.g.carri...@intel.com>
> > > > >
> > > > > > +__atomic_store_n(&sw->poll_lcores[n_lcores],
> > > > > > lcore,
> > > > > > +__ATOMIC_RELAXED);
> > > > > > +}
> > > > > > } else {
> > > > > > EVTIM_BUF_LOG_DBG("buffered an event timer expiry event");
> > > > > >
> > > > > > @@ -1011,6 +1016,7 @@ __swtim_arm_burst(const struct
> > > > > > rte_event_timer_adapter *adapter, uint32_t lcore_id =
> > > > > > rte_lcore_id(); struct rte_timer *tim, *tims[nb_evtims];
> > > > > > uint64_t cycles;
> > > > > > +int n_lcores;
> > > > > >
> > > > > > #ifdef RTE_LIBRTE_EVENTDEV_DEBUG
> > > > > > /* Check that the service is running. */ @@ -1033,8 +1039,10
> > > > > > @@ __swtim_arm_burst(const struct rte_event_timer_adapter
> > > > > > *adapter, if
> > > > > > (unlikely(rte_atomic16_test_and_set(&sw->in_use[lcore_id].v)))
> > > > > > { EVTIM_LOG_DBG("Adding lcore id = %u to list of lcores to
> > > > > poll",
> > > > > > lcore_id);
> > > > > > -sw->poll_lcores[sw->n_poll_lcores] = lcore_id;
> > > > > > -++sw->n_poll_lcores;
> > > > > > +n_lcores = __atomic_fetch_add(&sw->n_poll_lcores, 1,
> > > > > > +__ATOMIC_RELAXED); __atomic_store_n(&sw-
> > >poll_lcores[n_lcores],
> > > > > > +lcore_id, __ATOMIC_RELAXED);
> > > > > > }
> > > > > >
> > > > > > ret = rte_mempool_get_bulk(sw->tim_pool, (void **)tims,
> > > > > > --
> > > > > > 2.7.4
> > > >
