Re: [PATCH v3] eventdev/timer: fix overflow issue

[Jerin Jacob <jerinjacobk@gmail.com>]

On Thu, Feb 9, 2023 at 8:44 PM Erik Gabriel Carrillo
<erik.g.carrillo@intel.com> wrote:
>
> The software timer adapter converts event timer timeout ticks to a
> number of TSC cycles at which an rte_timer should expire. The
> computation uses an integer multiplication that can result in overflow.
>
> If necessary, reduce the timeout_nsecs value by the number of whole
> seconds it contains to keep the value of the multiplier within a
> range that will not result in overflow.  Add the saved value back later
> to get the final result. Also, move the logic that checks the timeout
> range into the function that performs the above computation.
>
> Fixes: 6750b21bd6af ("eventdev: add default software timer adapter")
> Cc: stable@dpdk.org
>
> Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>

Applied to dpdk-next-net-eventdev/for-main. Thanks


> ---
> v3:
> * Use integer operations instead of floating point, and use
>   rte_reciprocal_divide() for division.
>
> v2:
> * Fix implicit int to float conversion build warning on Clang
>
>  lib/eventdev/rte_event_timer_adapter.c | 97 ++++++++++++++++----------
>  1 file changed, 59 insertions(+), 38 deletions(-)
>
> diff --git a/lib/eventdev/rte_event_timer_adapter.c b/lib/eventdev/rte_event_timer_adapter.c
> index 7f4f347369..23eb1d4a7d 100644
> --- a/lib/eventdev/rte_event_timer_adapter.c
> +++ b/lib/eventdev/rte_event_timer_adapter.c
> @@ -18,6 +18,7 @@
>  #include <rte_timer.h>
>  #include <rte_service_component.h>
>  #include <rte_telemetry.h>
> +#include <rte_reciprocal.h>
>
>  #include "event_timer_adapter_pmd.h"
>  #include "eventdev_pmd.h"
> @@ -734,13 +735,51 @@ swtim_callback(struct rte_timer *tim)
>         }
>  }
>
> -static __rte_always_inline uint64_t
> +static __rte_always_inline int
>  get_timeout_cycles(struct rte_event_timer *evtim,
> -                  const struct rte_event_timer_adapter *adapter)
> +                  const struct rte_event_timer_adapter *adapter,
> +                  uint64_t *timeout_cycles)
>  {
> -       struct swtim *sw = swtim_pmd_priv(adapter);
> -       uint64_t timeout_ns = evtim->timeout_ticks * sw->timer_tick_ns;
> -       return timeout_ns * rte_get_timer_hz() / NSECPERSEC;
> +       static struct rte_reciprocal_u64 nsecpersec_inverse;
> +       static uint64_t timer_hz;
> +       uint64_t rem_cycles, secs_cycles = 0;
> +       uint64_t secs, timeout_nsecs;
> +       uint64_t nsecpersec;
> +       struct swtim *sw;
> +
> +       sw = swtim_pmd_priv(adapter);
> +       nsecpersec = (uint64_t)NSECPERSEC;
> +
> +       timeout_nsecs = evtim->timeout_ticks * sw->timer_tick_ns;
> +       if (timeout_nsecs > sw->max_tmo_ns)
> +               return -1;
> +       if (timeout_nsecs < sw->timer_tick_ns)
> +               return -2;
> +
> +       /* Set these values in the first invocation */
> +       if (!timer_hz) {
> +               timer_hz = rte_get_timer_hz();
> +               nsecpersec_inverse = rte_reciprocal_value_u64(nsecpersec);
> +       }
> +
> +       /* If timeout_nsecs > nsecpersec, decrease timeout_nsecs by the number
> +        * of whole seconds it contains and convert that value to a number
> +        * of cycles. This keeps timeout_nsecs in the interval [0..nsecpersec)
> +        * in order to avoid overflow when we later multiply by timer_hz.
> +        */
> +       if (timeout_nsecs > nsecpersec) {
> +               secs = rte_reciprocal_divide_u64(timeout_nsecs,
> +                                                &nsecpersec_inverse);
> +               secs_cycles = secs * timer_hz;
> +               timeout_nsecs -= secs * nsecpersec;
> +       }
> +
> +       rem_cycles = rte_reciprocal_divide_u64(timeout_nsecs * timer_hz,
> +                                              &nsecpersec_inverse);
> +
> +       *timeout_cycles = secs_cycles + rem_cycles;
> +
> +       return 0;
>  }
>
>  /* This function returns true if one or more (adapter) ticks have occurred since
> @@ -774,23 +813,6 @@ swtim_did_tick(struct swtim *sw)
>         return false;
>  }
>
> -/* Check that event timer timeout value is in range */
> -static __rte_always_inline int
> -check_timeout(struct rte_event_timer *evtim,
> -             const struct rte_event_timer_adapter *adapter)
> -{
> -       uint64_t tmo_nsec;
> -       struct swtim *sw = swtim_pmd_priv(adapter);
> -
> -       tmo_nsec = evtim->timeout_ticks * sw->timer_tick_ns;
> -       if (tmo_nsec > sw->max_tmo_ns)
> -               return -1;
> -       if (tmo_nsec < sw->timer_tick_ns)
> -               return -2;
> -
> -       return 0;
> -}
> -
>  /* Check that event timer event queue sched type matches destination event queue
>   * sched type
>   */
> @@ -1210,21 +1232,6 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,
>                         break;
>                 }
>
> -               ret = check_timeout(evtims[i], adapter);
> -               if (unlikely(ret == -1)) {
> -                       __atomic_store_n(&evtims[i]->state,
> -                                       RTE_EVENT_TIMER_ERROR_TOOLATE,
> -                                       __ATOMIC_RELAXED);
> -                       rte_errno = EINVAL;
> -                       break;
> -               } else if (unlikely(ret == -2)) {
> -                       __atomic_store_n(&evtims[i]->state,
> -                                       RTE_EVENT_TIMER_ERROR_TOOEARLY,
> -                                       __ATOMIC_RELAXED);
> -                       rte_errno = EINVAL;
> -                       break;
> -               }
> -
>                 if (unlikely(check_destination_event_queue(evtims[i],
>                                                            adapter) < 0)) {
>                         __atomic_store_n(&evtims[i]->state,
> @@ -1240,7 +1247,21 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,
>                 evtims[i]->impl_opaque[0] = (uintptr_t)tim;
>                 evtims[i]->impl_opaque[1] = (uintptr_t)adapter;
>
> -               cycles = get_timeout_cycles(evtims[i], adapter);
> +               ret = get_timeout_cycles(evtims[i], adapter, &cycles);
> +               if (unlikely(ret == -1)) {
> +                       __atomic_store_n(&evtims[i]->state,
> +                                       RTE_EVENT_TIMER_ERROR_TOOLATE,
> +                                       __ATOMIC_RELAXED);
> +                       rte_errno = EINVAL;
> +                       break;
> +               } else if (unlikely(ret == -2)) {
> +                       __atomic_store_n(&evtims[i]->state,
> +                                       RTE_EVENT_TIMER_ERROR_TOOEARLY,
> +                                       __ATOMIC_RELAXED);
> +                       rte_errno = EINVAL;
> +                       break;
> +               }
> +
>                 ret = rte_timer_alt_reset(sw->timer_data_id, tim, cycles,
>                                           type, lcore_id, NULL, evtims[i]);
>                 if (ret < 0) {
> --
> 2.23.0
>