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

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Date:   Wed, 24 Aug 2022 10:45:21 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Jerry Snitselaar <jsnitsel@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
        Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org
Subject: Re: [PATCH v2] dmaengine: idxd: avoid deadlock in
 process_misc_interrupts()


On 8/23/2022 5:54 PM, Jerry Snitselaar wrote:
> On Tue, Aug 23, 2022 at 09:46:19AM -0700, Dave Jiang wrote:
>> On 8/23/2022 9:37 AM, Jerry Snitselaar wrote:
>>> idxd_device_clear_state() now grabs the idxd->dev_lock
>>> itself, so don't grab the lock prior to calling it.
>>>
>>> This was seen in testing after dmar fault occurred on system,
>>> resulting in lockup stack traces.
>>>
>>> Cc: Fenghua Yu <fenghua.yu@...el.com>
>>> Cc: Dave Jiang <dave.jiang@...el.com>
>>> Cc: Vinod Koul <vkoul@...nel.org>
>>> Cc: dmaengine@...r.kernel.org
>>> Fixes: cf4ac3fef338 ("dmaengine: idxd: fix lockdep warning on device driver removal")
>>> Signed-off-by: Jerry Snitselaar <jsnitsel@...hat.com>
>> Thanks Jerry!
>>
>> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
>>
> I noticed another problem while looking at this. When the device ends
> up in the halted state, and needs an flr or system reset, it calls
> idxd_wqs_unmap_portal(). Then if you do a modprobe -r idxd, you hit
> the WARN_ON in devm_iounmap(), because the remove code path calls
> idxd_wq_portal_unmap(), and wq->portal is null. I'm not sure if it
> just needs a simple sanity check in drv_disable_wq() to avoid the call
> in the case that it has already been unmapped, or if more cleanup
> needs to be done, and possibly a state to differentiate between
> halted + soft reset possible, versus halted + flr or system reset
> needed.  You get multiple "Device is HALTED" messages during the
> removal as well.

Thanks!

Fenghua, can you please take a look at this when you have a chance? 
Thank you!


>
> Regards,
> Jerry
>