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);
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
