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From: Thomas Monjalon <thomas@monjalon.net>
To: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
Cc: dev@dpdk.org, Gavin.Hu@arm.com, rsanford@akamai.com,
	olivier.matz@6wind.com, stephen@networkplumber.org,
	bruce.richardson@intel.com, stable@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2] timer: fix race condition
Date: Wed, 19 Dec 2018 19:54:15 +0100	[thread overview]
Message-ID: <1710260.bNaUKXAX4B@xps> (raw)
In-Reply-To: <1545235774-9834-1-git-send-email-erik.g.carrillo@intel.com>

19/12/2018 17:09, 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 a
>     pending list or a 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>
> Reviewed-by: Gavin Hu <gavin.hu@arm.com>

+Cc: stable@dpdk.org

Applied, thanks

      reply	other threads:[~2018-12-19 18:54 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-29 18:53 [dpdk-dev] [PATCH 1/1] " Erik Gabriel Carrillo
2018-12-19  3:36 ` Thomas Monjalon
2018-12-19  7:57   ` Gavin Hu (Arm Technology China)
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 [this message]

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