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From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: Phil Yang <Phil.Yang@arm.com>,
	"Carrillo, Erik G" <erik.g.carrillo@intel.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Cc: "drc@linux.vnet.ibm.com" <drc@linux.vnet.ibm.com>,
	Ruifeng Wang <Ruifeng.Wang@arm.com>,
	Dharmik Thakkar <Dharmik.Thakkar@arm.com>,
	"stable@dpdk.org" <stable@dpdk.org>, nd <nd@arm.com>,
	"jerinj@marvell.com" <jerinj@marvell.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH 1/3] eventdev: fix race condition on timer list counter
Date: Thu, 2 Jul 2020 03:56:15 +0000	[thread overview]
Message-ID: <DB6PR0802MB2216D79C21F906E32850DB19986D0@DB6PR0802MB2216.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <VE1PR08MB4640D1AEF9AA9AF3CA312AB9E96D0@VE1PR08MB4640.eurprd08.prod.outlook.com>

<snip>
> >
> > >
> > > Hi Phil,
> > >
> > > Good catch - thanks for the fix.   I've commented in-line:
> > >
> > > > -----Original Message-----
> > > > From: Phil Yang <phil.yang@arm.com>
> > > > Sent: Friday, June 12, 2020 6:20 AM
> > > > To: dev@dpdk.org; Carrillo, Erik G <erik.g.carrillo@intel.com>
> > > > Cc: drc@linux.vnet.ibm.com; honnappa.nagarahalli@arm.com;
> > > > ruifeng.wang@arm.com; dharmik.thakkar@arm.com; nd@arm.com;
> > > > stable@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.carrillo@intel.com
> > > > Cc: stable@dpdk.org
> > > >
> > > > Signed-off-by: Phil Yang <phil.yang@arm.com>
> > > > Reviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
> > > > Reviewed-by: Ruifeng Wang <ruifeng.wang@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?

> 
> 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.carrillo@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
> >


  reply	other threads:[~2020-07-02  3:56 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12 11:19 Phil Yang
2020-06-12 11:19 ` [dpdk-dev] [PATCH 2/3] eventdev: use c11 atomics for lcore timer armed flag Phil Yang
2020-06-23 21:01   ` Carrillo, Erik G
2020-06-28 16:12     ` Phil Yang
2020-06-23 21:20   ` Stephen Hemminger
2020-06-23 21:31     ` Carrillo, Erik G
2020-06-28 16:32       ` Phil Yang
2020-06-12 11:19 ` [dpdk-dev] [PATCH 3/3] eventdev: relax smp barriers with c11 atomics Phil Yang
2020-06-22 10:12   ` Phil Yang
2020-06-23 19:38     ` Carrillo, Erik G
2020-06-28 17:33       ` Phil Yang
2020-06-29 18:07         ` Carrillo, Erik G
2020-06-18 15:17 ` [dpdk-dev] [PATCH 1/3] eventdev: fix race condition on timer list counter Carrillo, Erik G
2020-06-18 18:25   ` Honnappa Nagarahalli
2020-06-22  9:48     ` Phil Yang
2020-07-01 11:22       ` Jerin Jacob
2020-07-02  3:28         ` Phil Yang
2020-07-02  3:26     ` Phil Yang
2020-07-02  3:56       ` Honnappa Nagarahalli [this message]
2020-07-02 21:15         ` Carrillo, Erik G
2020-07-02 21:30           ` Honnappa Nagarahalli
2020-06-22  9:09   ` Phil Yang
2020-07-02  5:26 ` [dpdk-dev] [PATCH v2 1/4] " Phil Yang
2020-07-02  5:26   ` [dpdk-dev] [PATCH v2 2/4] eventdev: use c11 atomics for lcore timer armed flag Phil Yang
2020-07-02 20:21     ` Carrillo, Erik G
2020-07-02  5:26   ` [dpdk-dev] [PATCH v2 3/4] eventdev: remove redundant code Phil Yang
2020-07-03  3:35     ` Dharmik Thakkar
2020-07-02  5:26   ` [dpdk-dev] [PATCH v2 4/4] eventdev: relax smp barriers with c11 atomics Phil Yang
2020-07-02 20:30     ` Carrillo, Erik G
2020-07-03 10:50       ` Jerin Jacob
2020-07-06 10:04     ` Thomas Monjalon
2020-07-06 15:32       ` Phil Yang
2020-07-06 15:40         ` Thomas Monjalon
2020-07-07 11:13   ` [dpdk-dev] [PATCH v3 1/4] eventdev: fix race condition on timer list counter Phil Yang
2020-07-07 11:13     ` [dpdk-dev] [PATCH v3 2/4] eventdev: use C11 atomics for lcore timer armed flag Phil Yang
2020-07-07 11:13     ` [dpdk-dev] [PATCH v3 3/4] eventdev: remove redundant code Phil Yang
2020-07-07 11:13     ` [dpdk-dev] [PATCH v3 4/4] eventdev: relax smp barriers with C11 atomics Phil Yang
2020-07-07 14:29       ` Jerin Jacob
2020-07-07 15:56         ` Phil Yang
2020-07-07 15:54     ` [dpdk-dev] [PATCH v4 1/4] eventdev: fix race condition on timer list counter Phil Yang
2020-07-07 15:54       ` [dpdk-dev] [PATCH v4 2/4] eventdev: use C11 atomics for lcore timer armed flag Phil Yang
2020-07-07 15:54       ` [dpdk-dev] [PATCH v4 3/4] eventdev: remove redundant code Phil Yang
2020-07-07 15:54       ` [dpdk-dev] [PATCH v4 4/4] eventdev: relax smp barriers with C11 atomics Phil Yang
2020-07-08 13:30       ` [dpdk-dev] [PATCH v4 1/4] eventdev: fix race condition on timer list counter Jerin Jacob
2020-07-08 15:01         ` Thomas Monjalon

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