linux-kernel - Re: NULL ptr deref in wq_worker

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Message-ID: <alpine.DEB.2.21.1908071452350.24014@nanos.tec.linutronix.de>
Date:   Wed, 7 Aug 2019 14:56:01 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Austin Kim <austindh.kim@...il.com>
cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Sasha Levin <sashal@...nel.org>, peterz@...radead.org,
        mingo@...nel.org, tj@...nel.org, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: NULL ptr deref in wq_worker_sleeping on 4.19

On Wed, 7 Aug 2019, Austin Kim wrote:

  A: Because it messes up the order in which people normally read text.
  Q: Why is top-posting such a bad thing?
  A: Top-posting.
  Q: What is the most annoying thing in e-mail?

  A: No.
  Q: Should I include quotations after my reply?

  http://daringfireball.net/2007/07/on_top

> I wonder what kinds of workqueue is used in case of this panic.
> 
> If system workqueue(system_wq) is used for this case, it would be a
> help to replace it with high priority workqueue(system_highpri_wq). If
> panic disappers with high priority workqueue(system_highpri_wq), we
> would think about another scenario.

How would that help? As Sebastian explained, something overwrote memory or
it is a Use After Free. How would a high priority workqueue 'fix' that?

You need to find the root cause, which is either memory corruption or a use
after free.

Thanks,

	tglx