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Subject: Re: Question on taskqueue_drain
To: Sepherosa Ziehau <sepherosa@gmail.com>,
 "Somayajulu, David" <David.Somayajulu@cavium.com>
References: <BY2PR07MB14745123AC235B06BCD2987DEE190@BY2PR07MB1474.namprd07.prod.outlook.com>
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 <CAMOc5cxtSakeBhskbmfW4BxsbgdRDp22AVBYrDgReCP91YLY7g@mail.gmail.com>
Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>
From: Hans Petter Selasky <hps@selasky.org>
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Date: Wed, 19 Apr 2017 06:22:28 +0200
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On 04/19/17 05:37, Sepherosa Ziehau wrote:
> On Wed, Apr 19, 2017 at 10:39 AM, Somayajulu, David
> <David.Somayajulu@cavium.com> wrote:
>> Sorry what I meant to ask was, whether it is O.K to call taskqueue_drain(), when an MTX_DEF lock is grabbed prior to calling taskqueue_drain().
>>
>
> You will hit WITNESS, if the drain needs to wait; that's probably the
> best case.  If the lock will be acquired in the task being drained,
> this leads to deadlock.
>

Hi,

No sleeping functions like taskqueue_drain() can be called when the 
MTX_DEF lock is grabbed.

--HPS