<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).
>
> 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
