From: "Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>
To: Thomas Monjalon <thomas@monjalon.net>, "dev@dpdk.org" <dev@dpdk.org>
Cc: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>,
"rsanford@akamai.com" <rsanford@akamai.com>,
"olivier.matz@6wind.com" <olivier.matz@6wind.com>,
"stephen@networkplumber.org" <stephen@networkplumber.org>,
"bruce.richardson@intel.com" <bruce.richardson@intel.com>
Subject: Re: [dpdk-dev] [PATCH 1/1] timer: fix race condition
Date: Wed, 19 Dec 2018 07:57:03 +0000 [thread overview]
Message-ID: <VI1PR08MB3167D271D857C308183793A38FBE0@VI1PR08MB3167.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <3302607.WHYlCW4uPu@xps>
> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Thomas Monjalon
> Sent: Wednesday, December 19, 2018 11:37 AM
> To: dev@dpdk.org
> Cc: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>; rsanford@akamai.com;
> olivier.matz@6wind.com; stephen@networkplumber.org;
> bruce.richardson@intel.com
> Subject: Re: [dpdk-dev] [PATCH 1/1] timer: fix race condition
>
> Who could review this fix please?
>
> 29/11/2018 19:53, Erik Gabriel Carrillo:
> > rte_timer_manage() adds expired timers to a "run list", and walks the
> > list, transitioning each timer from the PENDING to the RUNNING state.
> > If another lcore resets or stops the timer at precisely this moment,
> > the timer state would instead be set to CONFIG by that other lcore,
> > which would cause timer_manage() to skip over it. This is expected
> > behavior.
> >
> > However, if a timer expires quickly enough, there exists the following
> > race condition that causes the timer_manage() routine to misinterpret
> > a timer in CONFIG state, resulting in lost timers:
> >
> > - Thread A:
> > - starts a timer with rte_timer_reset()
> > - the timer is moved to CONFIG state
> > - the spinlock associated with the appropriate skiplist is acquired
> > - timer is inserted into the skiplist
> > - the spinlock is released
> > - Thread B:
> > - executes rte_timer_manage()
> > - find above timer as expired, add it to run list
> > - walk run list, see above timer still in CONFIG state, unlink it from
> > run list and continue on
> > - Thread A:
> > - move timer to PENDING state
> > - return from rte_timer_reset()
> > - timer is now in PENDING state, but not actually linked into skiplist
Add "nor the run list"?
> > and will never get processed further by rte_timer_manage()
> >
> > This commit fixes this race condition by only releasing the spinlock
> > after the timer state has been transitioned from CONFIG to PENDING,
> > which prevents rte_timer_manage() from seeing an incorrect state.
> >
> > Fixes: 9b15ba895b9f ("timer: use a skip list")
> > Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
> > ---
> > lib/librte_timer/rte_timer.c | 28 ++++++++++++++--------------
> > 1 file changed, 14 insertions(+), 14 deletions(-)
> >
> > diff --git a/lib/librte_timer/rte_timer.c
> > b/lib/librte_timer/rte_timer.c index 590488c..30c7b0a 100644
> > --- a/lib/librte_timer/rte_timer.c
> > +++ b/lib/librte_timer/rte_timer.c
> > @@ -241,24 +241,17 @@ timer_get_prev_entries_for_node(struct
> rte_timer *tim, unsigned tim_lcore,
> > }
> > }
> >
> > -/*
> > - * add in list, lock if needed
> > +/* call with lock held as necessary
> > + * add in list
> > * timer must be in config state
> > * timer must not be in a list
> > */
> > static void
> > -timer_add(struct rte_timer *tim, unsigned tim_lcore, int
> > local_is_locked)
> > +timer_add(struct rte_timer *tim, unsigned int tim_lcore)
> > {
> > -unsigned lcore_id = rte_lcore_id();
> > unsigned lvl;
> > struct rte_timer *prev[MAX_SKIPLIST_DEPTH+1];
> >
> > -/* if timer needs to be scheduled on another core, we need to
> > - * lock the list; if it is on local core, we need to lock if
> > - * we are not called from rte_timer_manage() */
> > -if (tim_lcore != lcore_id || !local_is_locked)
> > -rte_spinlock_lock(&priv_timer[tim_lcore].list_lock);
> > -
> > /* find where exactly this element goes in the list of elements
> > * for each depth. */
> > timer_get_prev_entries(tim->expire, tim_lcore, prev); @@ -282,9
> > +275,6 @@ timer_add(struct rte_timer *tim, unsigned tim_lcore, int
> local_is_locked)
> > * NOTE: this is not atomic on 32-bit*/
> > priv_timer[tim_lcore].pending_head.expire = priv_timer[tim_lcore].\
> > pending_head.sl_next[0]->expire;
> > -
> > -if (tim_lcore != lcore_id || !local_is_locked)
> > -rte_spinlock_unlock(&priv_timer[tim_lcore].list_lock);
> > }
> >
> > /*
> > @@ -379,8 +369,15 @@ __rte_timer_reset(struct rte_timer *tim,
> uint64_t expire,
> > tim->f = fct;
> > tim->arg = arg;
> >
> > +/* if timer needs to be scheduled on another core, we need to
> > + * lock the destination list; if it is on local core, we need to lock if
> > + * we are not called from rte_timer_manage()
> > + */
> > +if (tim_lcore != lcore_id || !local_is_locked)
> > +rte_spinlock_lock(&priv_timer[tim_lcore].list_lock);
> > +
> > __TIMER_STAT_ADD(pending, 1);
> > -timer_add(tim, tim_lcore, local_is_locked);
> > +timer_add(tim, tim_lcore);
> >
> > /* update state: as we are in CONFIG state, only us can modify
> > * the state so we don't need to use cmpset() here */ @@ -389,6
> > +386,9 @@ __rte_timer_reset(struct rte_timer *tim, uint64_t expire,
> > status.owner = (int16_t)tim_lcore;
> > tim->status.u32 = status.u32;
> >
> > +if (tim_lcore != lcore_id || !local_is_locked)
> > +rte_spinlock_unlock(&priv_timer[tim_lcore].list_lock);
> > +
> > return 0;
> > }
> >
Other than the minor comment,
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
>
>
>
>
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next prev parent reply other threads:[~2018-12-19 7:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-29 18:53 Erik Gabriel Carrillo
2018-12-19 3:36 ` Thomas Monjalon
2018-12-19 7:57 ` Gavin Hu (Arm Technology China) [this message]
2018-12-19 16:11 ` Carrillo, Erik G
2018-12-19 16:09 ` [dpdk-dev] [PATCH v2] " Erik Gabriel Carrillo
2018-12-19 18:54 ` Thomas Monjalon
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