linux-kernel - Re: [PATCH v2] dmaengine: idxd: avoid deadlock in process_misc

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Date:   Wed, 24 Aug 2022 14:34:00 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Zhu, Tony" <tony.zhu@...el.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vinod Koul <vkoul@...nel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
Subject: Re: [PATCH v2] dmaengine: idxd: avoid deadlock in
 process_misc_interrupts()

On Wed, 2022-08-24 at 21:11 +0000, Yu, Fenghua wrote:
> Hi, Jerry,
> 
> > I see another potential issue. If a software reset is attempted
> > idxd_device_reinit()
> > will be called which walks the wqs, and if a wq has the state
> > IDXD_WQ_ENABLED it calls idxd_wq_enable(), but the first thing
> > idxd_wq_enable() does is see that the state is IDXD_WQ_ENABLED and
> > returns 0.
> > Without the wq enable command being sent, it will not be re-
> > enabled, yes?
> 
> Could you please describe how to reproduce the issues and test case?

Nothing special, just running dsa_user_test_runner.sh from idxd-config
(3.4.6.3) with intel_iommu=on,sm_on (default is lazy dma domain) on an
Intel supplied SPR system. During the run there is a dmar fault, halts
the device with it needing an flr reset. That is where the deadlock was
noticed. Then after the dsa_user_runner.sh fails, if you do modprobe -r
idxd, you hit the warning in devm_iounmap().

The idxd_device_reinit() case I haven't reproduced, I'm just looking at
the code.

I should note that I've only run into an issue with that model
of system. The other models of SPR systems don't hit an issue. This is
with a 6.0-rc1 kernel, and our kernel. I'm guessing there is an issue
with that model of system/fw. I've seen both fault reasons 0x50 and
0x58 when it faults.

Regards,
Jerry

> 
> Thanks.
> 
> -Fenghua