linux-kernel - Re: [PATCHSET wq/for-6.9] workqueue: Implement BH workqueue and convert several tasklet users

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Date: Mon, 29 Jan 2024 23:22:19 -1000
From: Tejun Heo <tj@...nel.org>
To: torvalds@...ux-foundation.org, mpatocka@...hat.com,
	Lai Jiangshan <jiangshanlai@...il.com>
Cc: linux-kernel@...r.kernel.org, dm-devel@...ts.linux.dev,
	msnitzer@...hat.com, ignat@...udflare.com, damien.lemoal@....com,
	houtao1@...wei.com, peterz@...radead.org, mingo@...nel.org,
	netdev@...r.kernel.org, allen.lkml@...il.com, kernel-team@...a.com
Subject: Re: [PATCHSET wq/for-6.9] workqueue: Implement BH workqueue and
 convert several tasklet users

Oops, forgot to cc Lai.

On Mon, Jan 29, 2024 at 11:11:47PM -1000, Tejun Heo wrote:
> Hello,
> 
> The only generic interface to execute asynchronously in the BH context is
> tasklet; however, it's marked deprecated and has some design flaws such as
> the execution code accessing the tasklet item after the execution is
> complete which can lead to subtle use-after-free in certain usage scenarios
> and less-developed flush and cancel mechanisms.
> 
> Mikulas Patocka recently reported that dm-crypt and dm-crypt are affected by
> the access-after-completion issue and suggested adding TASKLET_STATE_ONESHOT
> flag which selectively removes post-completion access while significantly
> limiting how the tasklet can be used in the following thread:
> 
>  http://lkml.kernel.org/r/82b964f0-c2c8-a2c6-5b1f-f3145dc2c8e5@redhat.com
> 
> Linus didn't like the approach and suggested extending workqueue to support
> execution from atomic context:
> 
>  http://lkml.kernel.org/r/CAHk-=wjDW53w4-YcSmgKC5RruiRLHmJ1sXeYdp_ZgVoBw=5byA@mail.gmail.com
> 
> As suggested, this patchset implements BH workqueues which are like regular
> workqueues but executes work items in the BH (softirq) context and converts
> several tasklet users.

Lai, the patchset is at:

 http://lkml.kernel.org/r/20240130091300.2968534-1-tj@kernel.org

I'd really appreciate if you can take a look.

Thanks.

-- 
tejun